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	$26.67	5.188%	$28.0536	$28.05	$28.05	$28.10
Purchase #2	$32.76	13.713%	$37.2524	$37.25	$37.25	$37.30
Purchase #3	$180.45	8.763%	$196.2628	$196.26	$196.25	$196.30
Purchase #4	$95.31	9.457%	$104.3235	$104.32	$104.30	$104.30
Purchase #5	$9.86	12.114%	$11.0544	$11.05	$11.05	$11.10
Purchase #6	$70.87	7.749%	$76.3617	$76.36	$76.35	$76.40
Purchase #7	$71.65	7.475%	$77.0058	$77.01	$77.00	$77.00
7 purchase totals =	$487.57		$530.3142	$530.30	$530.25	$530.50