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	$28.56	10.264%	$31.4914	$31.49	$31.50	$31.50
Purchase #2	$59.42	7.460%	$63.8527	$63.85	$63.85	$63.90
Purchase #3	$132.39	13.549%	$150.3275	$150.33	$150.35	$150.30
Purchase #4	$43.28	3.653%	$44.861	$44.86	$44.85	$44.90
Purchase #5	$238.86	6.484%	$254.3477	$254.35	$254.35	$254.30
Purchase #6	$128.62	8.782%	$139.9154	$139.92	$139.90	$139.90
Purchase #7	$176.38	4.513%	$184.34	$184.34	$184.35	$184.30
7 purchase totals =	$807.51		$869.1357	$869.14	$869.15	$869.10