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	$11.97	4.831%	$12.5483	$12.55	$12.55	$12.50
Purchase #2	$172.55	9.724%	$189.3288	$189.33	$189.35	$189.30
Purchase #3	$220.30	3.718%	$228.4908	$228.49	$228.50	$228.50
Purchase #4	$124.57	4.464%	$130.1308	$130.13	$130.15	$130.10
Purchase #5	$223.93	5.145%	$235.4512	$235.45	$235.45	$235.50
Purchase #6	$40.84	11.472%	$45.5252	$45.53	$45.55	$45.50
Purchase #7	$87.31	13.224%	$98.8559	$98.86	$98.85	$98.90
7 purchase totals =	$881.47		$940.3310	$940.34	$940.40	$940.30