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	$18.69	9.185%	$20.4067	$20.41	$20.40	$20.40
Purchase #2	$88.67	5.825%	$93.835	$93.84	$93.85	$93.80
Purchase #3	$33.45	12.426%	$37.6065	$37.61	$37.60	$37.60
Purchase #4	$155.92	6.103%	$165.4358	$165.44	$165.45	$165.40
Purchase #5	$95.51	9.628%	$104.7057	$104.71	$104.70	$104.70
Purchase #6	$248.60	4.405%	$259.5508	$259.55	$259.55	$259.60
Purchase #7	$166.26	3.624%	$172.2853	$172.29	$172.30	$172.30
7 purchase totals =	$807.10		$853.8258	$853.85	$853.85	$853.80