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	$16.56	12.172%	$18.5757	$18.58	$18.60	$18.60
Purchase #2	$112.74	7.660%	$121.3759	$121.38	$121.40	$121.40
Purchase #3	$126.34	4.481%	$132.0013	$132.00	$132.00	$132.00
Purchase #4	$45.59	11.700%	$50.924	$50.92	$50.90	$50.90
Purchase #5	$45.33	3.314%	$46.8322	$46.83	$46.85	$46.80
Purchase #6	$77.56	7.477%	$83.3592	$83.36	$83.35	$83.40
Purchase #7	$209.67	3.197%	$216.3731	$216.37	$216.35	$216.40
7 purchase totals =	$633.79		$669.4414	$669.44	$669.45	$669.50