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	$148.75	13.851%	$169.3534	$169.35	$169.35	$169.40
Purchase #2	$124.34	12.362%	$139.7109	$139.71	$139.70	$139.70
Purchase #3	$158.59	6.179%	$168.3893	$168.39	$168.40	$168.40
Purchase #4	$45.27	4.679%	$47.3882	$47.39	$47.40	$47.40
Purchase #5	$173.41	5.864%	$183.5788	$183.58	$183.60	$183.60
Purchase #6	$217.89	7.803%	$234.892	$234.89	$234.90	$234.90
Purchase #7	$7.35	6.755%	$7.8465	$7.85	$7.85	$7.80
7 purchase totals =	$875.60		$951.1591	$951.16	$951.20	$951.20