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	$131.98	3.241%	$136.2575	$136.26	$136.25	$136.30
Purchase #2	$161.62	11.535%	$180.2629	$180.26	$180.25	$180.30
Purchase #3	$156.96	11.741%	$175.3887	$175.39	$175.40	$175.40
Purchase #4	$18.67	11.123%	$20.7467	$20.75	$20.75	$20.70
Purchase #5	$203.73	9.286%	$222.6484	$222.65	$222.65	$222.60
Purchase #6	$201.70	10.204%	$222.2815	$222.28	$222.30	$222.30
Purchase #7	$153.34	12.506%	$172.5167	$172.52	$172.50	$172.50
7 purchase totals =	$1,028.00		$1,130.1024	$1,130.11	$1,130.10	$1,130.10