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	$246.43	13.466%	$279.6143	$279.61	$279.60	$279.60
Purchase #2	$55.64	12.808%	$62.7664	$62.77	$62.75	$62.80
Purchase #3	$157.32	3.223%	$162.3904	$162.39	$162.40	$162.40
Purchase #4	$215.25	7.588%	$231.5832	$231.58	$231.60	$231.60
Purchase #5	$103.49	3.121%	$106.7199	$106.72	$106.70	$106.70
Purchase #6	$132.53	10.874%	$146.9413	$146.94	$146.95	$146.90
Purchase #7	$197.96	13.103%	$223.8987	$223.90	$223.90	$223.90
7 purchase totals =	$1,108.62		$1,213.9142	$1,213.91	$1,213.90	$1,213.90