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	$73.85	5.644%	$78.0181	$78.02	$78.00	$78.00
Purchase #2	$122.43	11.500%	$136.5095	$136.51	$136.50	$136.50
Purchase #3	$37.61	11.451%	$41.9167	$41.92	$41.90	$41.90
Purchase #4	$182.31	9.807%	$200.1891	$200.19	$200.20	$200.20
Purchase #5	$54.91	7.105%	$58.8114	$58.81	$58.80	$58.80
Purchase #6	$95.34	5.146%	$100.2462	$100.25	$100.25	$100.20
Purchase #7	$113.43	9.633%	$124.3567	$124.36	$124.35	$124.40
7 purchase totals =	$679.88		$740.0477	$740.06	$740.00	$740.00