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	$228.93	8.638%	$248.705	$248.71	$248.70	$248.70
Purchase #2	$80.89	10.179%	$89.1238	$89.12	$89.10	$89.10
Purchase #3	$213.98	13.163%	$242.1462	$242.15	$242.15	$242.10
Purchase #4	$231.35	4.821%	$242.5034	$242.50	$242.50	$242.50
Purchase #5	$190.35	4.707%	$199.3098	$199.31	$199.30	$199.30
Purchase #6	$234.91	3.639%	$243.4584	$243.46	$243.45	$243.50
Purchase #7	$83.72	7.451%	$89.958	$89.96	$89.95	$90.00
7 purchase totals =	$1,264.13		$1,355.2046	$1,355.21	$1,355.15	$1,355.20