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	$115.70	13.791%	$131.6562	$131.66	$131.65	$131.70
Purchase #2	$203.85	9.562%	$223.3421	$223.34	$223.35	$223.30
Purchase #3	$20.34	4.633%	$21.2824	$21.28	$21.30	$21.30
Purchase #4	$93.92	10.637%	$103.9103	$103.91	$103.90	$103.90
Purchase #5	$209.94	7.604%	$225.9038	$225.90	$225.90	$225.90
Purchase #6	$38.33	8.714%	$41.6701	$41.67	$41.65	$41.70
Purchase #7	$9.64	11.247%	$10.7242	$10.72	$10.70	$10.70
7 purchase totals =	$691.72		$758.4891	$758.48	$758.45	$758.50