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	$129.61	11.457%	$144.4594	$144.46	$144.45	$144.50
Purchase #2	$242.30	12.327%	$272.1683	$272.17	$272.15	$272.20
Purchase #3	$194.52	3.559%	$201.443	$201.44	$201.45	$201.40
Purchase #4	$138.47	12.294%	$155.4935	$155.49	$155.50	$155.50
Purchase #5	$99.81	10.657%	$110.4468	$110.45	$110.45	$110.40
Purchase #6	$18.57	12.740%	$20.9358	$20.94	$20.95	$20.90
Purchase #7	$216.50	13.587%	$245.9159	$245.92	$245.90	$245.90
7 purchase totals =	$1,039.78		$1,150.8627	$1,150.87	$1,150.85	$1,150.80