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	$131.29	11.168%	$145.9525	$145.95	$145.95	$146.00
Purchase #2	$151.77	12.428%	$170.632	$170.63	$170.65	$170.60
Purchase #3	$60.56	13.789%	$68.9106	$68.91	$68.90	$68.90
Purchase #4	$80.43	11.246%	$89.4752	$89.48	$89.50	$89.50
Purchase #5	$12.29	4.358%	$12.8256	$12.83	$12.85	$12.80
Purchase #6	$143.83	8.461%	$155.9995	$156.00	$156.00	$156.00
Purchase #7	$132.66	12.168%	$148.8021	$148.80	$148.80	$148.80
7 purchase totals =	$712.83		$792.5975	$792.60	$792.65	$792.60