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	$46.34	10.369%	$51.145	$51.15	$51.15	$51.10
Purchase #2	$204.77	4.237%	$213.4461	$213.45	$213.45	$213.40
Purchase #3	$114.48	4.388%	$119.5034	$119.50	$119.50	$119.50
Purchase #4	$35.41	13.851%	$40.3146	$40.31	$40.30	$40.30
Purchase #5	$192.80	7.532%	$207.3217	$207.32	$207.30	$207.30
Purchase #6	$123.61	7.527%	$132.9141	$132.91	$132.90	$132.90
Purchase #7	$83.26	9.109%	$90.8442	$90.84	$90.85	$90.80
7 purchase totals =	$800.67		$855.4891	$855.48	$855.45	$855.30