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	$139.55	10.776%	$154.5879	$154.59	$154.60	$154.60
Purchase #2	$130.27	12.660%	$146.7622	$146.76	$146.75	$146.80
Purchase #3	$110.89	11.522%	$123.6667	$123.67	$123.65	$123.70
Purchase #4	$94.46	9.144%	$103.0974	$103.10	$103.10	$103.10
Purchase #5	$146.67	5.787%	$155.1578	$155.16	$155.15	$155.20
Purchase #6	$26.48	8.443%	$28.7157	$28.72	$28.70	$28.70
Purchase #7	$85.96	11.460%	$95.811	$95.81	$95.80	$95.80
7 purchase totals =	$734.28		$807.7987	$807.81	$807.75	$807.90