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	$75.69	13.443%	$85.865	$85.87	$85.85	$85.90
Purchase #2	$193.64	9.694%	$212.4115	$212.41	$212.40	$212.40
Purchase #3	$158.36	13.327%	$179.4646	$179.46	$179.45	$179.50
Purchase #4	$67.65	13.790%	$76.9789	$76.98	$77.00	$77.00
Purchase #5	$6.86	11.369%	$7.6399	$7.64	$7.65	$7.60
Purchase #6	$106.75	9.484%	$116.8742	$116.87	$116.85	$116.90
Purchase #7	$40.87	10.529%	$45.1732	$45.17	$45.15	$45.20
7 purchase totals =	$649.82		$724.4073	$724.40	$724.35	$724.50