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	$167.33	12.585%	$188.3885	$188.39	$188.40	$188.40
Purchase #2	$156.90	11.677%	$175.2212	$175.22	$175.20	$175.20
Purchase #3	$29.90	8.525%	$32.449	$32.45	$32.45	$32.40
Purchase #4	$12.58	9.635%	$13.7921	$13.79	$13.80	$13.80
Purchase #5	$108.50	4.706%	$113.606	$113.61	$113.60	$113.60
Purchase #6	$202.95	9.860%	$222.9609	$222.96	$222.95	$223.00
Purchase #7	$83.62	5.816%	$88.4833	$88.48	$88.50	$88.50
7 purchase totals =	$761.78		$834.9010	$834.90	$834.90	$834.90