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	$133.31	13.654%	$151.5121	$151.51	$151.50	$151.50
Purchase #2	$156.51	8.511%	$169.8306	$169.83	$169.85	$169.80
Purchase #3	$215.60	7.385%	$231.5221	$231.52	$231.50	$231.50
Purchase #4	$149.79	10.518%	$165.5449	$165.54	$165.55	$165.50
Purchase #5	$98.60	11.463%	$109.9025	$109.90	$109.90	$109.90
Purchase #6	$59.72	3.467%	$61.7905	$61.79	$61.80	$61.80
Purchase #7	$84.41	3.729%	$87.5576	$87.56	$87.55	$87.60
7 purchase totals =	$897.94		$977.6603	$977.65	$977.65	$977.60