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	$37.50	8.594%	$40.7228	$40.72	$40.70	$40.70
Purchase #2	$158.41	13.263%	$179.4199	$179.42	$179.40	$179.40
Purchase #3	$245.50	10.300%	$270.7865	$270.79	$270.80	$270.80
Purchase #4	$52.86	4.863%	$55.4306	$55.43	$55.45	$55.40
Purchase #5	$83.29	11.291%	$92.6943	$92.69	$92.70	$92.70
Purchase #6	$111.91	7.770%	$120.6054	$120.61	$120.60	$120.60
Purchase #7	$72.71	11.791%	$81.2832	$81.28	$81.30	$81.30
7 purchase totals =	$762.18		$840.9427	$840.94	$840.95	$840.90