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	$240.59	4.277%	$250.88	$250.88	$250.90	$250.90
Purchase #2	$85.41	6.647%	$91.0872	$91.09	$91.10	$91.10
Purchase #3	$191.75	11.164%	$213.157	$213.16	$213.15	$213.20
Purchase #4	$11.42	10.795%	$12.6528	$12.65	$12.65	$12.70
Purchase #5	$89.42	11.359%	$99.5772	$99.58	$99.60	$99.60
Purchase #6	$116.83	13.528%	$132.6348	$132.63	$132.65	$132.60
Purchase #7	$26.47	10.225%	$29.1766	$29.18	$29.20	$29.20
7 purchase totals =	$761.89		$829.1656	$829.17	$829.25	$829.30