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	$111.81	3.301%	$115.5008	$115.50	$115.50	$115.50
Purchase #2	$223.46	9.342%	$244.3356	$244.34	$244.35	$244.30
Purchase #3	$225.46	8.807%	$245.3163	$245.32	$245.30	$245.30
Purchase #4	$58.51	13.384%	$66.341	$66.34	$66.35	$66.30
Purchase #5	$35.67	6.335%	$37.9297	$37.93	$37.95	$37.90
Purchase #6	$138.59	3.584%	$143.5571	$143.56	$143.55	$143.60
Purchase #7	$79.64	10.546%	$88.0388	$88.04	$88.05	$88.00
7 purchase totals =	$873.14		$941.0193	$941.03	$941.05	$940.90