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	$28.96	12.164%	$32.4827	$32.48	$32.50	$32.50
Purchase #2	$134.25	5.127%	$141.133	$141.13	$141.15	$141.10
Purchase #3	$94.68	7.311%	$101.6021	$101.60	$101.60	$101.60
Purchase #4	$155.81	13.848%	$177.3866	$177.39	$177.40	$177.40
Purchase #5	$6.89	8.319%	$7.4632	$7.46	$7.45	$7.50
Purchase #6	$197.81	5.732%	$209.1485	$209.15	$209.15	$209.10
Purchase #7	$234.49	9.123%	$255.8825	$255.88	$255.90	$255.90
7 purchase totals =	$852.89		$925.0986	$925.09	$925.15	$925.10