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	$125.55	4.370%	$131.0365	$131.04	$131.05	$131.00
Purchase #2	$159.56	13.181%	$180.5916	$180.59	$180.60	$180.60
Purchase #3	$65.68	10.803%	$72.7754	$72.78	$72.80	$72.80
Purchase #4	$77.58	7.532%	$83.4233	$83.42	$83.40	$83.40
Purchase #5	$141.79	11.862%	$158.6091	$158.61	$158.60	$158.60
Purchase #6	$68.30	13.482%	$77.5082	$77.51	$77.50	$77.50
Purchase #7	$227.25	4.172%	$236.7309	$236.73	$236.75	$236.70
7 purchase totals =	$865.71		$940.6750	$940.68	$940.70	$940.60