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	$67.32	6.862%	$71.9395	$71.94	$71.95	$71.90
Purchase #2	$7.37	3.777%	$7.6484	$7.65	$7.65	$7.60
Purchase #3	$227.29	11.581%	$253.6125	$253.61	$253.60	$253.60
Purchase #4	$33.80	12.850%	$38.1433	$38.14	$38.15	$38.10
Purchase #5	$126.69	9.112%	$138.234	$138.23	$138.25	$138.20
Purchase #6	$234.70	8.603%	$254.8912	$254.89	$254.90	$254.90
Purchase #7	$103.81	7.368%	$111.4587	$111.46	$111.45	$111.50
7 purchase totals =	$800.98		$875.9276	$875.92	$875.95	$875.80