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	$47.29	7.676%	$50.92	$50.92	$50.90	$50.90
Purchase #2	$188.64	12.137%	$211.5352	$211.54	$211.55	$211.50
Purchase #3	$203.90	8.685%	$221.6087	$221.61	$221.60	$221.60
Purchase #4	$246.42	7.478%	$264.8473	$264.85	$264.85	$264.80
Purchase #5	$143.27	3.517%	$148.3088	$148.31	$148.30	$148.30
Purchase #6	$185.35	12.808%	$209.0896	$209.09	$209.10	$209.10
Purchase #7	$36.55	10.515%	$40.3932	$40.39	$40.40	$40.40
7 purchase totals =	$1,051.42		$1,146.7028	$1,146.71	$1,146.70	$1,146.60