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	$116.82	12.404%	$131.3104	$131.31	$131.30	$131.30
Purchase #2	$30.53	12.503%	$34.3472	$34.35	$34.35	$34.30
Purchase #3	$120.94	3.797%	$125.5321	$125.53	$125.55	$125.50
Purchase #4	$144.35	4.232%	$150.4589	$150.46	$150.45	$150.50
Purchase #5	$237.45	7.476%	$255.2018	$255.20	$255.20	$255.20
Purchase #6	$40.42	4.347%	$42.1771	$42.18	$42.20	$42.20
Purchase #7	$118.70	10.606%	$131.2893	$131.29	$131.30	$131.30
7 purchase totals =	$809.21		$870.3168	$870.32	$870.35	$870.30