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	$149.38	3.767%	$155.0071	$155.01	$155.00	$155.00
Purchase #2	$188.47	6.142%	$200.0458	$200.05	$200.05	$200.00
Purchase #3	$195.59	13.368%	$221.7365	$221.74	$221.75	$221.70
Purchase #4	$140.61	13.869%	$160.1112	$160.11	$160.10	$160.10
Purchase #5	$214.28	3.871%	$222.5748	$222.57	$222.55	$222.60
Purchase #6	$18.70	7.803%	$20.1592	$20.16	$20.15	$20.20
Purchase #7	$55.36	5.594%	$58.4568	$58.46	$58.45	$58.50
7 purchase totals =	$962.39		$1,038.0914	$1,038.10	$1,038.05	$1,038.10