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	$87.64	3.732%	$90.9107	$90.91	$90.90	$90.90
Purchase #2	$36.58	11.623%	$40.8317	$40.83	$40.85	$40.80
Purchase #3	$13.71	8.349%	$14.8546	$14.85	$14.85	$14.90
Purchase #4	$117.95	6.400%	$125.4988	$125.50	$125.50	$125.50
Purchase #5	$10.84	9.690%	$11.8904	$11.89	$11.90	$11.90
Purchase #6	$164.30	10.780%	$182.0115	$182.01	$182.00	$182.00
Purchase #7	$179.44	12.855%	$202.507	$202.51	$202.50	$202.50
7 purchase totals =	$610.46		$668.5047	$668.50	$668.50	$668.50