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	$86.86	3.788%	$90.1503	$90.15	$90.15	$90.20
Purchase #2	$48.77	13.123%	$55.1701	$55.17	$55.15	$55.20
Purchase #3	$183.56	6.423%	$195.3501	$195.35	$195.35	$195.40
Purchase #4	$94.70	11.269%	$105.3717	$105.37	$105.35	$105.40
Purchase #5	$32.46	7.857%	$35.0104	$35.01	$35.00	$35.00
Purchase #6	$37.72	7.619%	$40.5939	$40.59	$40.60	$40.60
Purchase #7	$119.50	12.618%	$134.5785	$134.58	$134.60	$134.60
7 purchase totals =	$603.57		$656.2250	$656.22	$656.20	$656.40