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	$151.43	3.148%	$156.197	$156.20	$156.20	$156.20
Purchase #2	$135.82	4.614%	$142.0867	$142.09	$142.10	$142.10
Purchase #3	$109.48	13.708%	$124.4875	$124.49	$124.50	$124.50
Purchase #4	$150.49	3.365%	$155.554	$155.55	$155.55	$155.60
Purchase #5	$151.49	13.867%	$172.4971	$172.50	$172.50	$172.50
Purchase #6	$222.76	5.770%	$235.6133	$235.61	$235.60	$235.60
Purchase #7	$10.50	11.656%	$11.7239	$11.72	$11.70	$11.70
7 purchase totals =	$931.97		$998.1595	$998.16	$998.15	$998.20