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	$171.35	12.325%	$192.4689	$192.47	$192.45	$192.50
Purchase #2	$236.31	4.304%	$246.4808	$246.48	$246.50	$246.50
Purchase #3	$220.95	8.307%	$239.3043	$239.30	$239.30	$239.30
Purchase #4	$52.29	13.564%	$59.3826	$59.38	$59.40	$59.40
Purchase #5	$19.90	4.449%	$20.7854	$20.79	$20.80	$20.80
Purchase #6	$11.53	12.196%	$12.9362	$12.94	$12.95	$12.90
Purchase #7	$159.55	9.378%	$174.5126	$174.51	$174.50	$174.50
7 purchase totals =	$871.88		$945.8708	$945.87	$945.90	$945.90