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	$80.26	8.780%	$87.3068	$87.31	$87.30	$87.30
Purchase #2	$132.33	13.544%	$150.2528	$150.25	$150.25	$150.30
Purchase #3	$130.47	7.135%	$139.779	$139.78	$139.80	$139.80
Purchase #4	$55.76	7.388%	$59.8795	$59.88	$59.90	$59.90
Purchase #5	$26.30	10.522%	$29.0673	$29.07	$29.05	$29.10
Purchase #6	$14.61	11.406%	$16.2764	$16.28	$16.30	$16.30
Purchase #7	$152.58	9.761%	$167.4733	$167.47	$167.45	$167.50
7 purchase totals =	$592.31		$650.0351	$650.04	$650.05	$650.20