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	$90.40	13.297%	$102.4205	$102.42	$102.40	$102.40
Purchase #2	$185.63	7.647%	$199.8251	$199.83	$199.85	$199.80
Purchase #3	$111.52	8.155%	$120.6145	$120.61	$120.60	$120.60
Purchase #4	$144.80	5.575%	$152.8726	$152.87	$152.85	$152.90
Purchase #5	$160.63	7.412%	$172.5359	$172.54	$172.55	$172.50
Purchase #6	$37.49	6.669%	$39.9902	$39.99	$40.00	$40.00
Purchase #7	$197.86	5.148%	$208.0458	$208.05	$208.05	$208.00
7 purchase totals =	$928.33		$996.3046	$996.31	$996.30	$996.20