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	$33.61	12.444%	$37.7924	$37.79	$37.80	$37.80
Purchase #2	$33.56	12.370%	$37.7114	$37.71	$37.70	$37.70
Purchase #3	$242.67	11.190%	$269.8248	$269.82	$269.80	$269.80
Purchase #4	$134.30	4.409%	$140.2213	$140.22	$140.20	$140.20
Purchase #5	$140.84	12.263%	$158.1112	$158.11	$158.10	$158.10
Purchase #6	$130.29	10.679%	$144.2037	$144.20	$144.20	$144.20
Purchase #7	$212.90	7.334%	$228.5141	$228.51	$228.50	$228.50
7 purchase totals =	$928.17		$1,016.3789	$1,016.36	$1,016.30	$1,016.30