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	$119.81	9.723%	$131.4591	$131.46	$131.45	$131.50
Purchase #2	$37.89	11.420%	$42.217	$42.22	$42.20	$42.20
Purchase #3	$135.30	11.223%	$150.4847	$150.48	$150.50	$150.50
Purchase #4	$120.72	13.395%	$136.8904	$136.89	$136.90	$136.90
Purchase #5	$204.37	13.697%	$232.3626	$232.36	$232.35	$232.40
Purchase #6	$22.54	12.460%	$25.3485	$25.35	$25.35	$25.30
Purchase #7	$163.52	10.324%	$180.4018	$180.40	$180.40	$180.40
7 purchase totals =	$804.15		$899.1641	$899.16	$899.15	$899.20