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	$18.98	13.380%	$21.5195	$21.52	$21.50	$21.50
Purchase #2	$193.32	8.316%	$209.3965	$209.40	$209.40	$209.40
Purchase #3	$215.26	6.449%	$229.1421	$229.14	$229.15	$229.10
Purchase #4	$247.47	3.811%	$256.9011	$256.90	$256.90	$256.90
Purchase #5	$113.25	9.194%	$123.6622	$123.66	$123.65	$123.70
Purchase #6	$152.82	10.184%	$168.3832	$168.38	$168.40	$168.40
Purchase #7	$243.47	4.837%	$255.2466	$255.25	$255.25	$255.20
7 purchase totals =	$1,184.57		$1,264.2512	$1,264.25	$1,264.25	$1,264.20