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	$234.31	8.454%	$254.1186	$254.12	$254.10	$254.10
Purchase #2	$58.48	6.233%	$62.1251	$62.13	$62.15	$62.10
Purchase #3	$173.93	10.598%	$192.3631	$192.36	$192.35	$192.40
Purchase #4	$242.78	3.459%	$251.1778	$251.18	$251.20	$251.20
Purchase #5	$127.39	3.546%	$131.9072	$131.91	$131.90	$131.90
Purchase #6	$45.51	11.711%	$50.8397	$50.84	$50.85	$50.80
Purchase #7	$34.47	7.770%	$37.1483	$37.15	$37.15	$37.10
7 purchase totals =	$916.87		$979.6798	$979.69	$979.70	$979.60