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	$206.91	12.628%	$233.0386	$233.04	$233.05	$233.00
Purchase #2	$76.75	11.816%	$85.8188	$85.82	$85.80	$85.80
Purchase #3	$36.43	11.358%	$40.5677	$40.57	$40.55	$40.60
Purchase #4	$103.33	6.273%	$109.8119	$109.81	$109.80	$109.80
Purchase #5	$30.52	10.451%	$33.7096	$33.71	$33.70	$33.70
Purchase #6	$21.34	9.830%	$23.4377	$23.44	$23.45	$23.40
Purchase #7	$136.37	11.816%	$152.4835	$152.48	$152.50	$152.50
7 purchase totals =	$611.65		$678.8678	$678.87	$678.85	$678.80