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	$109.78	12.781%	$123.811	$123.81	$123.80	$123.80
Purchase #2	$124.83	3.105%	$128.706	$128.71	$128.70	$128.70
Purchase #3	$207.44	11.761%	$231.837	$231.84	$231.85	$231.80
Purchase #4	$152.34	10.503%	$168.3403	$168.34	$168.35	$168.30
Purchase #5	$81.42	11.475%	$90.7629	$90.76	$90.75	$90.80
Purchase #6	$46.71	7.118%	$50.0348	$50.03	$50.05	$50.00
Purchase #7	$73.97	5.163%	$77.7891	$77.79	$77.80	$77.80
7 purchase totals =	$796.49		$871.2811	$871.28	$871.30	$871.20