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	$248.38	12.290%	$278.9059	$278.91	$278.90	$278.90
Purchase #2	$205.85	11.596%	$229.7204	$229.72	$229.70	$229.70
Purchase #3	$199.85	11.160%	$222.1533	$222.15	$222.15	$222.20
Purchase #4	$106.43	10.393%	$117.4913	$117.49	$117.50	$117.50
Purchase #5	$128.46	13.614%	$145.9485	$145.95	$145.95	$145.90
Purchase #6	$87.39	7.447%	$93.8979	$93.90	$93.90	$93.90
Purchase #7	$32.83	9.308%	$35.8858	$35.89	$35.90	$35.90
7 purchase totals =	$1,009.19		$1,124.0031	$1,124.01	$1,124.00	$1,124.00