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	$202.98	9.624%	$222.5148	$222.51	$222.50	$222.50
Purchase #2	$44.68	3.718%	$46.3412	$46.34	$46.35	$46.30
Purchase #3	$106.83	11.313%	$118.9157	$118.92	$118.90	$118.90
Purchase #4	$195.50	13.554%	$221.9981	$222.00	$222.00	$222.00
Purchase #5	$15.95	11.133%	$17.7257	$17.73	$17.75	$17.70
Purchase #6	$97.99	13.532%	$111.25	$111.25	$111.25	$111.30
Purchase #7	$82.78	3.668%	$85.8164	$85.82	$85.80	$85.80
7 purchase totals =	$746.71		$824.5619	$824.57	$824.55	$824.50