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	$17.95	12.502%	$20.1941	$20.19	$20.20	$20.20
Purchase #2	$42.81	5.420%	$45.1303	$45.13	$45.15	$45.10
Purchase #3	$67.75	7.394%	$72.7594	$72.76	$72.75	$72.80
Purchase #4	$24.27	8.432%	$26.3164	$26.32	$26.30	$26.30
Purchase #5	$106.82	12.232%	$119.8862	$119.89	$119.90	$119.90
Purchase #6	$35.57	13.380%	$40.3293	$40.33	$40.35	$40.30
Purchase #7	$178.77	3.255%	$184.589	$184.59	$184.60	$184.60
7 purchase totals =	$473.94		$509.2047	$509.21	$509.25	$509.20