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	$164.84	12.752%	$185.8604	$185.86	$185.85	$185.90
Purchase #2	$71.95	5.850%	$76.1591	$76.16	$76.15	$76.20
Purchase #3	$241.80	4.708%	$253.1839	$253.18	$253.20	$253.20
Purchase #4	$27.86	8.477%	$30.2217	$30.22	$30.20	$30.20
Purchase #5	$138.48	3.159%	$142.8546	$142.85	$142.85	$142.90
Purchase #6	$80.75	6.340%	$85.8696	$85.87	$85.85	$85.90
Purchase #7	$155.69	11.632%	$173.7999	$173.80	$173.80	$173.80
7 purchase totals =	$881.37		$947.9492	$947.94	$947.90	$948.10