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	$33.87	11.756%	$37.8518	$37.85	$37.85	$37.90
Purchase #2	$72.46	9.336%	$79.2249	$79.22	$79.20	$79.20
Purchase #3	$30.29	13.797%	$34.4691	$34.47	$34.45	$34.50
Purchase #4	$31.42	4.691%	$32.8939	$32.89	$32.90	$32.90
Purchase #5	$177.84	10.128%	$195.8516	$195.85	$195.85	$195.90
Purchase #6	$55.89	7.217%	$59.9236	$59.92	$59.90	$59.90
Purchase #7	$124.34	11.808%	$139.0221	$139.02	$139.00	$139.00
7 purchase totals =	$526.11		$579.2370	$579.22	$579.15	$579.30