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	$245.38	4.415%	$256.2135	$256.21	$256.20	$256.20
Purchase #2	$50.53	7.759%	$54.4506	$54.45	$54.45	$54.50
Purchase #3	$129.87	13.523%	$147.4323	$147.43	$147.45	$147.40
Purchase #4	$231.46	4.175%	$241.1235	$241.12	$241.10	$241.10
Purchase #5	$40.98	7.240%	$43.947	$43.95	$43.95	$43.90
Purchase #6	$169.25	7.468%	$181.8896	$181.89	$181.90	$181.90
Purchase #7	$164.43	11.802%	$183.836	$183.84	$183.85	$183.80
7 purchase totals =	$1,031.90		$1,108.8925	$1,108.89	$1,108.90	$1,108.80