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	$33.60	5.386%	$35.4097	$35.41	$35.40	$35.40
Purchase #2	$147.52	11.521%	$164.5158	$164.52	$164.50	$164.50
Purchase #3	$146.26	13.554%	$166.0841	$166.08	$166.10	$166.10
Purchase #4	$222.61	4.618%	$232.8901	$232.89	$232.90	$232.90
Purchase #5	$40.42	5.353%	$42.5837	$42.58	$42.60	$42.60
Purchase #6	$126.58	9.837%	$139.0317	$139.03	$139.05	$139.00
Purchase #7	$78.51	12.167%	$88.0623	$88.06	$88.05	$88.10
7 purchase totals =	$795.50		$868.5774	$868.57	$868.60	$868.60