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	$245.71	6.187%	$260.9121	$260.91	$260.90	$260.90
Purchase #2	$88.28	3.528%	$91.3945	$91.39	$91.40	$91.40
Purchase #3	$85.29	3.335%	$88.1344	$88.13	$88.15	$88.10
Purchase #4	$230.91	10.799%	$255.846	$255.85	$255.85	$255.80
Purchase #5	$45.91	8.149%	$49.6512	$49.65	$49.65	$49.70
Purchase #6	$111.63	4.537%	$116.6947	$116.69	$116.70	$116.70
Purchase #7	$118.90	10.452%	$131.3274	$131.33	$131.35	$131.30
7 purchase totals =	$926.63		$993.9603	$993.95	$994.00	$993.90