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	$20.79	5.265%	$21.8846	$21.88	$21.90	$21.90
Purchase #2	$55.28	5.816%	$58.4951	$58.50	$58.50	$58.50
Purchase #3	$112.66	7.263%	$120.8425	$120.84	$120.85	$120.80
Purchase #4	$206.41	10.259%	$227.5856	$227.59	$227.60	$227.60
Purchase #5	$37.77	3.571%	$39.1188	$39.12	$39.10	$39.10
Purchase #6	$152.35	10.813%	$168.8236	$168.82	$168.80	$168.80
Purchase #7	$32.95	7.379%	$35.3814	$35.38	$35.40	$35.40
7 purchase totals =	$618.21		$672.1316	$672.13	$672.15	$672.10