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	$72.37	13.156%	$81.891	$81.89	$81.90	$81.90
Purchase #2	$110.89	9.828%	$121.7883	$121.79	$121.80	$121.80
Purchase #3	$242.38	11.459%	$270.1543	$270.15	$270.15	$270.20
Purchase #4	$101.61	10.139%	$111.9122	$111.91	$111.90	$111.90
Purchase #5	$77.96	6.513%	$83.0375	$83.04	$83.05	$83.00
Purchase #6	$6.72	10.725%	$7.4407	$7.44	$7.45	$7.40
Purchase #7	$184.94	13.207%	$209.365	$209.37	$209.35	$209.40
7 purchase totals =	$796.87		$885.5890	$885.59	$885.60	$885.60