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	$203.48	12.166%	$228.2354	$228.24	$228.25	$228.20
Purchase #2	$45.39	6.297%	$48.2482	$48.25	$48.25	$48.20
Purchase #3	$202.75	8.682%	$220.3528	$220.35	$220.35	$220.40
Purchase #4	$52.59	13.715%	$59.8027	$59.80	$59.80	$59.80
Purchase #5	$191.60	11.340%	$213.3274	$213.33	$213.35	$213.30
Purchase #6	$113.53	6.479%	$120.8856	$120.89	$120.90	$120.90
Purchase #7	$45.78	10.337%	$50.5123	$50.51	$50.50	$50.50
7 purchase totals =	$855.12		$941.3644	$941.37	$941.40	$941.30