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	$87.93	3.326%	$90.8546	$90.85	$90.85	$90.90
Purchase #2	$111.87	7.822%	$120.6205	$120.62	$120.60	$120.60
Purchase #3	$193.42	8.426%	$209.7176	$209.72	$209.70	$209.70
Purchase #4	$131.86	6.245%	$140.0947	$140.09	$140.10	$140.10
Purchase #5	$76.67	7.630%	$82.5199	$82.52	$82.50	$82.50
Purchase #6	$92.44	7.840%	$99.6873	$99.69	$99.70	$99.70
Purchase #7	$168.83	7.794%	$181.9886	$181.99	$182.00	$182.00
7 purchase totals =	$863.02		$925.4832	$925.48	$925.45	$925.50