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	$63.72	10.664%	$70.5151	$70.52	$70.50	$70.50
Purchase #2	$246.56	13.502%	$279.8505	$279.85	$279.85	$279.90
Purchase #3	$129.77	7.242%	$139.1679	$139.17	$139.15	$139.20
Purchase #4	$195.25	11.851%	$218.3891	$218.39	$218.40	$218.40
Purchase #5	$32.88	11.294%	$36.5935	$36.59	$36.60	$36.60
Purchase #6	$150.58	11.736%	$168.2521	$168.25	$168.25	$168.30
Purchase #7	$34.50	13.458%	$39.143	$39.14	$39.15	$39.10
7 purchase totals =	$853.26		$951.9112	$951.91	$951.90	$952.00