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	$236.80	13.845%	$269.585	$269.59	$269.60	$269.60
Purchase #2	$31.93	6.328%	$33.9505	$33.95	$33.95	$34.00
Purchase #3	$35.77	4.386%	$37.3389	$37.34	$37.35	$37.30
Purchase #4	$185.26	12.368%	$208.173	$208.17	$208.15	$208.20
Purchase #5	$139.61	9.644%	$153.074	$153.07	$153.05	$153.10
Purchase #6	$73.65	4.771%	$77.1638	$77.16	$77.15	$77.20
Purchase #7	$38.44	7.468%	$41.3107	$41.31	$41.30	$41.30
7 purchase totals =	$741.46		$820.5959	$820.59	$820.55	$820.70