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	$149.67	3.206%	$154.4684	$154.47	$154.45	$154.50
Purchase #2	$154.87	11.125%	$172.0993	$172.10	$172.10	$172.10
Purchase #3	$32.57	7.622%	$35.0525	$35.05	$35.05	$35.10
Purchase #4	$149.88	11.674%	$167.377	$167.38	$167.40	$167.40
Purchase #5	$37.45	8.184%	$40.5149	$40.51	$40.50	$40.50
Purchase #6	$179.96	7.222%	$192.9567	$192.96	$192.95	$193.00
Purchase #7	$131.98	4.748%	$138.2464	$138.25	$138.25	$138.20
7 purchase totals =	$836.38		$900.7152	$900.72	$900.70	$900.80