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	$154.86	10.240%	$170.7177	$170.72	$170.70	$170.70
Purchase #2	$58.35	12.302%	$65.5282	$65.53	$65.55	$65.50
Purchase #3	$78.42	12.696%	$88.3762	$88.38	$88.40	$88.40
Purchase #4	$30.58	4.568%	$31.9769	$31.98	$32.00	$32.00
Purchase #5	$161.84	6.854%	$172.9325	$172.93	$172.95	$172.90
Purchase #6	$31.31	5.136%	$32.9181	$32.92	$32.90	$32.90
Purchase #7	$94.47	11.847%	$105.6619	$105.66	$105.65	$105.70
7 purchase totals =	$609.83		$668.1115	$668.12	$668.15	$668.10