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	$36.37	13.580%	$41.309	$41.31	$41.30	$41.30
Purchase #2	$29.82	5.493%	$31.458	$31.46	$31.45	$31.50
Purchase #3	$51.68	13.124%	$58.4625	$58.46	$58.45	$58.50
Purchase #4	$104.67	11.846%	$117.0692	$117.07	$117.05	$117.10
Purchase #5	$84.43	6.609%	$90.01	$90.01	$90.00	$90.00
Purchase #6	$221.31	11.265%	$246.2406	$246.24	$246.25	$246.20
Purchase #7	$76.53	11.664%	$85.4565	$85.46	$85.45	$85.50
7 purchase totals =	$604.81		$670.0058	$670.01	$669.95	$670.10