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	$167.70	12.245%	$188.2349	$188.23	$188.25	$188.20
Purchase #2	$45.56	6.456%	$48.5014	$48.50	$48.50	$48.50
Purchase #3	$169.33	6.636%	$180.5667	$180.57	$180.55	$180.60
Purchase #4	$6.29	13.292%	$7.1261	$7.13	$7.15	$7.10
Purchase #5	$102.28	3.470%	$105.8291	$105.83	$105.85	$105.80
Purchase #6	$34.66	3.853%	$35.9954	$36.00	$36.00	$36.00
Purchase #7	$88.84	12.114%	$99.6021	$99.60	$99.60	$99.60
7 purchase totals =	$614.66		$665.8557	$665.86	$665.90	$665.80