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	$57.31	7.311%	$61.4999	$61.50	$61.50	$61.50
Purchase #2	$53.62	12.624%	$60.389	$60.39	$60.40	$60.40
Purchase #3	$240.50	8.299%	$260.4591	$260.46	$260.45	$260.50
Purchase #4	$98.31	8.783%	$106.9446	$106.94	$106.95	$106.90
Purchase #5	$95.78	13.377%	$108.5925	$108.59	$108.60	$108.60
Purchase #6	$64.39	11.677%	$71.9088	$71.91	$71.90	$71.90
Purchase #7	$164.39	5.573%	$173.5515	$173.55	$173.55	$173.60
7 purchase totals =	$774.30		$843.3454	$843.34	$843.35	$843.40