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	$119.31	4.364%	$124.5167	$124.52	$124.50	$124.50
Purchase #2	$87.61	3.626%	$90.7867	$90.79	$90.80	$90.80
Purchase #3	$139.64	6.369%	$148.5337	$148.53	$148.55	$148.50
Purchase #4	$33.39	5.216%	$35.1316	$35.13	$35.15	$35.10
Purchase #5	$211.46	12.840%	$238.6115	$238.61	$238.60	$238.60
Purchase #6	$173.37	10.796%	$192.087	$192.09	$192.10	$192.10
Purchase #7	$18.79	13.599%	$21.3453	$21.35	$21.35	$21.30
7 purchase totals =	$783.57		$851.0125	$851.02	$851.05	$850.90