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	$139.49	6.338%	$148.3309	$148.33	$148.35	$148.30
Purchase #2	$129.90	5.102%	$136.5275	$136.53	$136.55	$136.50
Purchase #3	$96.83	9.168%	$105.7074	$105.71	$105.70	$105.70
Purchase #4	$191.91	13.536%	$217.8869	$217.89	$217.90	$217.90
Purchase #5	$248.38	13.143%	$281.0246	$281.02	$281.00	$281.00
Purchase #6	$38.66	10.351%	$42.6617	$42.66	$42.65	$42.70
Purchase #7	$149.80	10.835%	$166.0308	$166.03	$166.05	$166.00
7 purchase totals =	$994.97		$1,098.1698	$1,098.17	$1,098.20	$1,098.10