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	$88.67	12.171%	$99.462	$99.46	$99.45	$99.50
Purchase #2	$84.82	8.147%	$91.7303	$91.73	$91.75	$91.70
Purchase #3	$223.93	4.200%	$233.3351	$233.34	$233.35	$233.30
Purchase #4	$146.72	6.306%	$155.9722	$155.97	$155.95	$156.00
Purchase #5	$204.39	9.848%	$224.5183	$224.52	$224.50	$224.50
Purchase #6	$135.52	13.549%	$153.8816	$153.88	$153.90	$153.90
Purchase #7	$20.30	8.494%	$22.0243	$22.02	$22.00	$22.00
7 purchase totals =	$904.35		$980.9238	$980.92	$980.90	$980.90