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	$223.26	12.307%	$250.7366	$250.74	$250.75	$250.70
Purchase #2	$95.27	10.683%	$105.4477	$105.45	$105.45	$105.40
Purchase #3	$178.91	11.117%	$198.7994	$198.80	$198.80	$198.80
Purchase #4	$84.54	7.533%	$90.9084	$90.91	$90.90	$90.90
Purchase #5	$122.49	11.433%	$136.4943	$136.49	$136.50	$136.50
Purchase #6	$160.40	3.522%	$166.0493	$166.05	$166.05	$166.00
Purchase #7	$48.78	3.336%	$50.4073	$50.41	$50.40	$50.40
7 purchase totals =	$913.65		$998.8430	$998.85	$998.85	$998.70