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	$244.83	12.548%	$275.5513	$275.55	$275.55	$275.60
Purchase #2	$164.30	13.172%	$185.9416	$185.94	$185.95	$185.90
Purchase #3	$206.31	10.643%	$228.2676	$228.27	$228.25	$228.30
Purchase #4	$111.91	7.650%	$120.4711	$120.47	$120.45	$120.50
Purchase #5	$218.28	12.195%	$244.8992	$244.90	$244.90	$244.90
Purchase #6	$63.36	13.465%	$71.8914	$71.89	$71.90	$71.90
Purchase #7	$51.34	3.629%	$53.2031	$53.20	$53.20	$53.20
7 purchase totals =	$1,060.33		$1,180.2253	$1,180.22	$1,180.20	$1,180.30