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	$87.54	12.535%	$98.5131	$98.51	$98.50	$98.50
Purchase #2	$236.35	7.393%	$253.8234	$253.82	$253.80	$253.80
Purchase #3	$128.96	12.312%	$144.8376	$144.84	$144.85	$144.80
Purchase #4	$43.60	10.476%	$48.1675	$48.17	$48.15	$48.20
Purchase #5	$146.46	6.664%	$156.2201	$156.22	$156.20	$156.20
Purchase #6	$123.66	5.617%	$130.606	$130.61	$130.60	$130.60
Purchase #7	$36.31	6.850%	$38.7972	$38.80	$38.80	$38.80
7 purchase totals =	$802.88		$870.9649	$870.97	$870.90	$870.90