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	$18.49	10.441%	$20.4205	$20.42	$20.40	$20.40
Purchase #2	$48.50	8.306%	$52.5284	$52.53	$52.55	$52.50
Purchase #3	$182.56	10.762%	$202.2071	$202.21	$202.20	$202.20
Purchase #4	$17.69	10.823%	$19.6046	$19.60	$19.60	$19.60
Purchase #5	$52.33	12.769%	$59.012	$59.01	$59.00	$59.00
Purchase #6	$101.90	7.749%	$109.7962	$109.80	$109.80	$109.80
Purchase #7	$51.81	7.644%	$55.7704	$55.77	$55.75	$55.80
7 purchase totals =	$473.28		$519.3392	$519.34	$519.30	$519.30