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	$22.72	12.297%	$25.5139	$25.51	$25.50	$25.50
Purchase #2	$178.29	12.718%	$200.9649	$200.96	$200.95	$201.00
Purchase #3	$80.26	8.803%	$87.3253	$87.33	$87.35	$87.30
Purchase #4	$37.87	12.424%	$42.575	$42.58	$42.60	$42.60
Purchase #5	$137.42	10.568%	$151.9425	$151.94	$151.95	$151.90
Purchase #6	$245.82	4.524%	$256.9409	$256.94	$256.95	$256.90
Purchase #7	$36.89	3.466%	$38.1686	$38.17	$38.15	$38.20
7 purchase totals =	$739.27		$803.4311	$803.43	$803.45	$803.40