Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$229.59	6.719%	$245.0162	$245.02	$245.00	$245.00
Purchase #2	$107.58	8.621%	$116.8545	$116.85	$116.85	$116.90
Purchase #3	$123.57	9.497%	$135.3054	$135.31	$135.30	$135.30
Purchase #4	$244.76	11.626%	$273.2158	$273.22	$273.20	$273.20
Purchase #5	$112.82	12.283%	$126.6777	$126.68	$126.70	$126.70
Purchase #6	$157.94	4.667%	$165.3111	$165.31	$165.30	$165.30
Purchase #7	$78.55	13.864%	$89.4402	$89.44	$89.45	$89.40
7 purchase totals =	$1,054.81		$1,151.8209	$1,151.83	$1,151.80	$1,151.80