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	$15.33	3.143%	$15.8118	$15.81	$15.80	$15.80
Purchase #2	$111.50	7.782%	$120.1769	$120.18	$120.20	$120.20
Purchase #3	$6.54	8.172%	$7.0744	$7.07	$7.05	$7.10
Purchase #4	$59.50	13.645%	$67.6188	$67.62	$67.60	$67.60
Purchase #5	$88.61	13.664%	$100.7177	$100.72	$100.70	$100.70
Purchase #6	$207.37	10.351%	$228.8349	$228.83	$228.85	$228.80
Purchase #7	$39.74	8.258%	$43.0217	$43.02	$43.00	$43.00
7 purchase totals =	$528.59		$583.2562	$583.25	$583.20	$583.20