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	$37.27	9.276%	$40.7272	$40.73	$40.75	$40.70
Purchase #2	$250.43	5.611%	$264.4816	$264.48	$264.50	$264.50
Purchase #3	$133.40	10.302%	$147.1429	$147.14	$147.15	$147.10
Purchase #4	$160.50	3.180%	$165.6039	$165.60	$165.60	$165.60
Purchase #5	$75.38	7.741%	$81.2152	$81.22	$81.20	$81.20
Purchase #6	$45.25	7.120%	$48.4718	$48.47	$48.45	$48.50
Purchase #7	$191.96	6.403%	$204.2512	$204.25	$204.25	$204.30
7 purchase totals =	$894.19		$951.8938	$951.89	$951.90	$951.90