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	$52.79	13.449%	$59.8897	$59.89	$59.90	$59.90
Purchase #2	$123.27	10.256%	$135.9126	$135.91	$135.90	$135.90
Purchase #3	$116.29	8.213%	$125.8409	$125.84	$125.85	$125.80
Purchase #4	$42.41	12.153%	$47.5641	$47.56	$47.55	$47.60
Purchase #5	$231.46	9.629%	$253.7473	$253.75	$253.75	$253.70
Purchase #6	$23.86	11.133%	$26.5163	$26.52	$26.50	$26.50
Purchase #7	$82.43	10.243%	$90.8733	$90.87	$90.85	$90.90
7 purchase totals =	$672.51		$740.3442	$740.34	$740.30	$740.30