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	$39.31	8.217%	$42.5401	$42.54	$42.55	$42.50
Purchase #2	$76.94	13.831%	$87.5816	$87.58	$87.60	$87.60
Purchase #3	$25.69	12.174%	$28.8175	$28.82	$28.80	$28.80
Purchase #4	$242.80	13.659%	$275.9641	$275.96	$275.95	$276.00
Purchase #5	$76.54	10.449%	$84.5377	$84.54	$84.55	$84.50
Purchase #6	$57.78	10.193%	$63.6695	$63.67	$63.65	$63.70
Purchase #7	$101.51	9.858%	$111.5169	$111.52	$111.50	$111.50
7 purchase totals =	$620.57		$694.6274	$694.63	$694.60	$694.60