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	$166.77	3.635%	$172.8321	$172.83	$172.85	$172.80
Purchase #2	$232.67	13.455%	$263.9757	$263.98	$264.00	$264.00
Purchase #3	$54.83	11.125%	$60.9298	$60.93	$60.95	$60.90
Purchase #4	$77.52	10.777%	$85.8743	$85.87	$85.85	$85.90
Purchase #5	$33.82	4.801%	$35.4437	$35.44	$35.45	$35.40
Purchase #6	$6.90	13.485%	$7.8305	$7.83	$7.85	$7.80
Purchase #7	$24.82	5.557%	$26.1992	$26.20	$26.20	$26.20
7 purchase totals =	$597.33		$653.0853	$653.08	$653.15	$653.00