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	$127.75	3.640%	$132.4001	$132.40	$132.40	$132.40
Purchase #2	$80.90	5.473%	$85.3277	$85.33	$85.35	$85.30
Purchase #3	$132.38	11.832%	$148.0432	$148.04	$148.05	$148.00
Purchase #4	$131.90	8.763%	$143.4584	$143.46	$143.45	$143.50
Purchase #5	$103.51	12.863%	$116.8245	$116.82	$116.80	$116.80
Purchase #6	$241.90	3.433%	$250.2044	$250.20	$250.20	$250.20
Purchase #7	$25.93	8.130%	$28.0381	$28.04	$28.05	$28.00
7 purchase totals =	$844.27		$904.2964	$904.29	$904.30	$904.20