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	$31.28	5.249%	$32.9219	$32.92	$32.90	$32.90
Purchase #2	$65.75	13.113%	$74.3718	$74.37	$74.35	$74.40
Purchase #3	$113.37	9.797%	$124.4769	$124.48	$124.50	$124.50
Purchase #4	$53.76	5.250%	$56.5824	$56.58	$56.60	$56.60
Purchase #5	$48.67	11.558%	$54.2953	$54.30	$54.30	$54.30
Purchase #6	$82.89	10.199%	$91.344	$91.34	$91.35	$91.30
Purchase #7	$71.98	7.721%	$77.5376	$77.54	$77.55	$77.50
7 purchase totals =	$467.70		$511.5299	$511.53	$511.55	$511.50