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	$152.95	12.390%	$171.9005	$171.90	$171.90	$171.90
Purchase #2	$249.60	11.804%	$279.0628	$279.06	$279.05	$279.10
Purchase #3	$250.99	10.869%	$278.2701	$278.27	$278.25	$278.30
Purchase #4	$6.93	13.686%	$7.8784	$7.88	$7.90	$7.90
Purchase #5	$37.34	5.763%	$39.4919	$39.49	$39.50	$39.50
Purchase #6	$154.60	10.520%	$170.8639	$170.86	$170.85	$170.90
Purchase #7	$26.34	4.287%	$27.4692	$27.47	$27.45	$27.50
7 purchase totals =	$878.75		$974.9368	$974.93	$974.90	$975.10