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	$240.97	12.147%	$270.2406	$270.24	$270.25	$270.20
Purchase #2	$232.28	3.672%	$240.8093	$240.81	$240.80	$240.80
Purchase #3	$92.66	11.212%	$103.049	$103.05	$103.05	$103.00
Purchase #4	$72.38	7.755%	$77.9931	$77.99	$78.00	$78.00
Purchase #5	$225.97	13.105%	$255.5834	$255.58	$255.60	$255.60
Purchase #6	$216.96	3.184%	$223.868	$223.87	$223.85	$223.90
Purchase #7	$65.55	9.873%	$72.0218	$72.02	$72.00	$72.00
7 purchase totals =	$1,146.77		$1,243.5652	$1,243.56	$1,243.55	$1,243.50