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	$136.29	5.122%	$143.2708	$143.27	$143.25	$143.30
Purchase #2	$215.95	10.450%	$238.5168	$238.52	$238.50	$238.50
Purchase #3	$96.99	13.291%	$109.8809	$109.88	$109.90	$109.90
Purchase #4	$25.63	11.742%	$28.6395	$28.64	$28.65	$28.60
Purchase #5	$26.77	5.150%	$28.1487	$28.15	$28.15	$28.10
Purchase #6	$33.50	6.346%	$35.6259	$35.63	$35.65	$35.60
Purchase #7	$78.45	11.537%	$87.5008	$87.50	$87.50	$87.50
7 purchase totals =	$613.58		$671.5834	$671.59	$671.60	$671.50