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	$118.89	6.692%	$126.8461	$126.85	$126.85	$126.80
Purchase #2	$219.48	8.685%	$238.5418	$238.54	$238.55	$238.50
Purchase #3	$97.58	13.354%	$110.6108	$110.61	$110.60	$110.60
Purchase #4	$87.67	13.400%	$99.4178	$99.42	$99.40	$99.40
Purchase #5	$122.63	11.321%	$136.5129	$136.51	$136.50	$136.50
Purchase #6	$32.77	7.535%	$35.2392	$35.24	$35.25	$35.20
Purchase #7	$49.34	8.221%	$53.3962	$53.40	$53.40	$53.40
7 purchase totals =	$728.36		$800.5648	$800.57	$800.55	$800.40