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	$123.32	12.773%	$139.0717	$139.07	$139.05	$139.10
Purchase #2	$37.62	13.224%	$42.5949	$42.59	$42.60	$42.60
Purchase #3	$182.87	8.119%	$197.7172	$197.72	$197.70	$197.70
Purchase #4	$168.74	5.420%	$177.8857	$177.89	$177.90	$177.90
Purchase #5	$166.84	7.193%	$178.8408	$178.84	$178.85	$178.80
Purchase #6	$245.55	10.205%	$270.6084	$270.61	$270.60	$270.60
Purchase #7	$53.96	5.410%	$56.8792	$56.88	$56.90	$56.90
7 purchase totals =	$978.90		$1,063.5979	$1,063.60	$1,063.60	$1,063.60