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	$35.91	4.424%	$37.4987	$37.50	$37.50	$37.50
Purchase #2	$40.45	5.858%	$42.8196	$42.82	$42.80	$42.80
Purchase #3	$149.94	10.848%	$166.2055	$166.21	$166.20	$166.20
Purchase #4	$54.59	11.865%	$61.0671	$61.07	$61.05	$61.10
Purchase #5	$106.85	12.202%	$119.8878	$119.89	$119.90	$119.90
Purchase #6	$239.96	12.160%	$269.1391	$269.14	$269.15	$269.10
Purchase #7	$175.61	12.730%	$197.9652	$197.97	$197.95	$198.00
7 purchase totals =	$803.31		$894.5830	$894.60	$894.55	$894.60