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	$166.98	3.370%	$172.6072	$172.61	$172.60	$172.60
Purchase #2	$31.70	3.770%	$32.8951	$32.90	$32.90	$32.90
Purchase #3	$83.41	6.757%	$89.046	$89.05	$89.05	$89.00
Purchase #4	$105.34	7.474%	$113.2131	$113.21	$113.20	$113.20
Purchase #5	$208.87	8.111%	$225.8114	$225.81	$225.80	$225.80
Purchase #6	$213.38	3.422%	$220.6819	$220.68	$220.70	$220.70
Purchase #7	$82.86	5.535%	$87.4463	$87.45	$87.45	$87.40
7 purchase totals =	$892.54		$941.7010	$941.71	$941.70	$941.60