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	$242.67	11.312%	$270.1208	$270.12	$270.10	$270.10
Purchase #2	$100.30	11.208%	$111.5416	$111.54	$111.55	$111.50
Purchase #3	$244.73	12.496%	$275.3115	$275.31	$275.30	$275.30
Purchase #4	$218.94	6.290%	$232.7113	$232.71	$232.70	$232.70
Purchase #5	$25.80	10.513%	$28.5124	$28.51	$28.50	$28.50
Purchase #6	$16.69	13.564%	$18.9538	$18.95	$18.95	$19.00
Purchase #7	$128.30	4.374%	$133.9118	$133.91	$133.90	$133.90
7 purchase totals =	$977.43		$1,071.0632	$1,071.05	$1,071.00	$1,071.00