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	$49.87	12.425%	$56.0663	$56.07	$56.05	$56.10
Purchase #2	$19.77	3.858%	$20.5327	$20.53	$20.55	$20.50
Purchase #3	$37.72	12.127%	$42.2943	$42.29	$42.30	$42.30
Purchase #4	$249.52	10.524%	$275.7795	$275.78	$275.80	$275.80
Purchase #5	$88.71	7.422%	$95.2941	$95.29	$95.30	$95.30
Purchase #6	$33.31	3.420%	$34.4492	$34.45	$34.45	$34.40
Purchase #7	$130.99	6.401%	$139.3747	$139.37	$139.35	$139.40
7 purchase totals =	$609.89		$663.7908	$663.78	$663.80	$663.80