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	$186.39	11.743%	$208.2778	$208.28	$208.30	$208.30
Purchase #2	$183.74	6.640%	$195.9403	$195.94	$195.95	$195.90
Purchase #3	$250.47	10.254%	$276.1532	$276.15	$276.15	$276.20
Purchase #4	$210.57	13.479%	$238.9527	$238.95	$238.95	$239.00
Purchase #5	$40.50	13.285%	$45.8804	$45.88	$45.90	$45.90
Purchase #6	$222.27	8.193%	$240.4806	$240.48	$240.50	$240.50
Purchase #7	$43.91	13.436%	$49.8097	$49.81	$49.80	$49.80
7 purchase totals =	$1,137.85		$1,255.4947	$1,255.49	$1,255.55	$1,255.60