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	$202.94	4.634%	$212.3442	$212.34	$212.35	$212.30
Purchase #2	$161.80	10.351%	$178.5479	$178.55	$178.55	$178.50
Purchase #3	$136.61	10.843%	$151.4226	$151.42	$151.40	$151.40
Purchase #4	$37.83	6.433%	$40.2636	$40.26	$40.25	$40.30
Purchase #5	$93.26	8.636%	$101.3139	$101.31	$101.30	$101.30
Purchase #6	$151.73	9.102%	$165.5405	$165.54	$165.55	$165.50
Purchase #7	$18.83	3.668%	$19.5207	$19.52	$19.50	$19.50
7 purchase totals =	$803.00		$868.9534	$868.94	$868.90	$868.80