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	$102.56	3.455%	$106.1034	$106.10	$106.10	$106.10
Purchase #2	$167.94	13.388%	$190.4238	$190.42	$190.40	$190.40
Purchase #3	$246.99	13.164%	$279.5038	$279.50	$279.50	$279.50
Purchase #4	$20.78	9.177%	$22.687	$22.69	$22.70	$22.70
Purchase #5	$218.83	11.163%	$243.258	$243.26	$243.25	$243.30
Purchase #6	$33.60	12.513%	$37.8044	$37.80	$37.80	$37.80
Purchase #7	$58.75	3.872%	$61.0248	$61.02	$61.00	$61.00
7 purchase totals =	$849.45		$940.8052	$940.79	$940.75	$940.80