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	$118.33	10.607%	$130.8813	$130.88	$130.90	$130.90
Purchase #2	$124.31	13.290%	$140.8308	$140.83	$140.85	$140.80
Purchase #3	$59.61	3.320%	$61.5891	$61.59	$61.60	$61.60
Purchase #4	$147.33	7.774%	$158.7834	$158.78	$158.80	$158.80
Purchase #5	$118.53	7.434%	$127.3415	$127.34	$127.35	$127.30
Purchase #6	$38.56	5.521%	$40.6889	$40.69	$40.70	$40.70
Purchase #7	$13.77	6.593%	$14.6779	$14.68	$14.70	$14.70
7 purchase totals =	$620.44		$674.7929	$674.79	$674.90	$674.80