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	$6.92	6.142%	$7.345	$7.35	$7.35	$7.30
Purchase #2	$110.65	11.546%	$123.4256	$123.43	$123.45	$123.40
Purchase #3	$137.64	6.652%	$146.7958	$146.80	$146.80	$146.80
Purchase #4	$96.57	7.826%	$104.1276	$104.13	$104.15	$104.10
Purchase #5	$96.44	9.346%	$105.4533	$105.45	$105.45	$105.50
Purchase #6	$35.73	13.297%	$40.481	$40.48	$40.50	$40.50
Purchase #7	$27.25	8.669%	$29.6123	$29.61	$29.60	$29.60
7 purchase totals =	$511.20		$557.2406	$557.25	$557.30	$557.20