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	$34.63	8.333%	$37.5157	$37.52	$37.50	$37.50
Purchase #2	$220.46	12.274%	$247.5193	$247.52	$247.50	$247.50
Purchase #3	$155.38	13.123%	$175.7705	$175.77	$175.75	$175.80
Purchase #4	$10.89	5.194%	$11.4556	$11.46	$11.45	$11.50
Purchase #5	$110.69	11.672%	$123.6097	$123.61	$123.60	$123.60
Purchase #6	$161.79	12.716%	$182.3632	$182.36	$182.35	$182.40
Purchase #7	$40.52	3.683%	$42.0124	$42.01	$42.00	$42.00
7 purchase totals =	$734.36		$820.2464	$820.25	$820.15	$820.30