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	$227.78	12.709%	$256.7286	$256.73	$256.75	$256.70
Purchase #2	$164.63	4.683%	$172.3396	$172.34	$172.35	$172.30
Purchase #3	$128.83	3.412%	$133.2257	$133.23	$133.25	$133.20
Purchase #4	$100.98	10.275%	$111.3557	$111.36	$111.35	$111.40
Purchase #5	$16.61	5.437%	$17.5131	$17.51	$17.50	$17.50
Purchase #6	$197.49	5.561%	$208.4724	$208.47	$208.45	$208.50
Purchase #7	$229.52	13.814%	$261.2259	$261.23	$261.25	$261.20
7 purchase totals =	$1,065.84		$1,160.8610	$1,160.87	$1,160.90	$1,160.80