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	$38.95	7.171%	$41.7431	$41.74	$41.75	$41.70
Purchase #2	$185.49	9.544%	$203.1932	$203.19	$203.20	$203.20
Purchase #3	$70.80	11.314%	$78.8103	$78.81	$78.80	$78.80
Purchase #4	$203.33	3.620%	$210.6905	$210.69	$210.70	$210.70
Purchase #5	$153.37	8.408%	$166.2653	$166.27	$166.25	$166.30
Purchase #6	$85.30	4.799%	$89.3935	$89.39	$89.40	$89.40
Purchase #7	$11.88	12.821%	$13.4031	$13.40	$13.40	$13.40
7 purchase totals =	$749.12		$803.4990	$803.49	$803.50	$803.50