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	$221.38	4.603%	$231.5701	$231.57	$231.55	$231.60
Purchase #2	$44.46	8.869%	$48.4032	$48.40	$48.40	$48.40
Purchase #3	$155.41	9.503%	$170.1786	$170.18	$170.20	$170.20
Purchase #4	$218.50	11.785%	$244.2502	$244.25	$244.25	$244.30
Purchase #5	$55.59	10.552%	$61.4559	$61.46	$61.45	$61.50
Purchase #6	$86.78	9.786%	$95.2723	$95.27	$95.25	$95.30
Purchase #7	$117.68	8.520%	$127.7063	$127.71	$127.70	$127.70
7 purchase totals =	$899.80		$978.8366	$978.84	$978.80	$979.00