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	$32.80	8.150%	$35.4732	$35.47	$35.45	$35.50
Purchase #2	$205.26	7.148%	$219.932	$219.93	$219.95	$219.90
Purchase #3	$209.63	3.827%	$217.6525	$217.65	$217.65	$217.70
Purchase #4	$37.62	11.451%	$41.9279	$41.93	$41.95	$41.90
Purchase #5	$237.40	7.652%	$255.5658	$255.57	$255.55	$255.60
Purchase #6	$10.50	9.252%	$11.4715	$11.47	$11.45	$11.50
Purchase #7	$35.77	12.535%	$40.2538	$40.25	$40.25	$40.30
7 purchase totals =	$768.98		$822.2767	$822.27	$822.25	$822.40