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	$238.44	7.145%	$255.4765	$255.48	$255.50	$255.50
Purchase #2	$40.67	10.206%	$44.8208	$44.82	$44.80	$44.80
Purchase #3	$216.48	10.174%	$238.5047	$238.50	$238.50	$238.50
Purchase #4	$39.27	7.406%	$42.1783	$42.18	$42.20	$42.20
Purchase #5	$56.55	5.403%	$59.6054	$59.61	$59.60	$59.60
Purchase #6	$198.92	13.305%	$225.3863	$225.39	$225.40	$225.40
Purchase #7	$48.29	10.491%	$53.3561	$53.36	$53.35	$53.40
7 purchase totals =	$838.62		$919.3281	$919.34	$919.35	$919.40