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	$225.59	13.442%	$255.9138	$255.91	$255.90	$255.90
Purchase #2	$100.59	12.512%	$113.1758	$113.18	$113.20	$113.20
Purchase #3	$247.90	6.514%	$264.0482	$264.05	$264.05	$264.00
Purchase #4	$65.37	6.323%	$69.5033	$69.50	$69.50	$69.50
Purchase #5	$56.88	10.204%	$62.684	$62.68	$62.70	$62.70
Purchase #6	$13.39	13.187%	$15.1557	$15.16	$15.15	$15.20
Purchase #7	$17.90	5.388%	$18.8645	$18.86	$18.85	$18.90
7 purchase totals =	$727.62		$799.3453	$799.34	$799.35	$799.40