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	$41.56	13.392%	$47.1257	$47.13	$47.15	$47.10
Purchase #2	$239.37	13.676%	$272.1062	$272.11	$272.10	$272.10
Purchase #3	$77.71	3.666%	$80.5588	$80.56	$80.55	$80.60
Purchase #4	$48.60	9.618%	$53.2743	$53.27	$53.25	$53.30
Purchase #5	$175.56	8.746%	$190.9145	$190.91	$190.90	$190.90
Purchase #6	$30.37	10.408%	$33.5309	$33.53	$33.55	$33.50
Purchase #7	$114.85	13.224%	$130.0378	$130.04	$130.05	$130.00
7 purchase totals =	$728.02		$807.5482	$807.55	$807.55	$807.50