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	$11.80	5.610%	$12.462	$12.46	$12.45	$12.50
Purchase #2	$34.93	12.376%	$39.2529	$39.25	$39.25	$39.30
Purchase #3	$31.34	3.775%	$32.5231	$32.52	$32.50	$32.50
Purchase #4	$188.81	9.558%	$206.8565	$206.86	$206.85	$206.90
Purchase #5	$170.26	8.817%	$185.2718	$185.27	$185.25	$185.30
Purchase #6	$36.60	11.379%	$40.7647	$40.76	$40.75	$40.80
Purchase #7	$69.27	7.449%	$74.4299	$74.43	$74.45	$74.40
7 purchase totals =	$543.01		$591.5609	$591.55	$591.50	$591.70