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	$47.73	11.389%	$53.166	$53.17	$53.15	$53.20
Purchase #2	$234.68	11.499%	$261.6659	$261.67	$261.65	$261.70
Purchase #3	$136.57	13.786%	$155.3975	$155.40	$155.40	$155.40
Purchase #4	$124.83	11.731%	$139.4738	$139.47	$139.45	$139.50
Purchase #5	$189.59	11.766%	$211.8972	$211.90	$211.90	$211.90
Purchase #6	$29.44	11.186%	$32.7332	$32.73	$32.75	$32.70
Purchase #7	$137.35	12.155%	$154.0449	$154.04	$154.05	$154.00
7 purchase totals =	$900.19		$1,008.3785	$1,008.38	$1,008.35	$1,008.40