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	$36.29	5.616%	$38.328	$38.33	$38.35	$38.30
Purchase #2	$140.98	7.431%	$151.4562	$151.46	$151.45	$151.50
Purchase #3	$170.38	12.142%	$191.0675	$191.07	$191.05	$191.10
Purchase #4	$35.27	5.276%	$37.1308	$37.13	$37.15	$37.10
Purchase #5	$158.99	5.198%	$167.2543	$167.25	$167.25	$167.30
Purchase #6	$80.70	7.457%	$86.7178	$86.72	$86.70	$86.70
Purchase #7	$220.82	10.536%	$244.0856	$244.09	$244.10	$244.10
7 purchase totals =	$843.43		$916.0402	$916.05	$916.05	$916.10