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	$164.38	4.403%	$171.6177	$171.62	$171.60	$171.60
Purchase #2	$178.49	6.470%	$190.0383	$190.04	$190.05	$190.00
Purchase #3	$111.87	4.239%	$116.6122	$116.61	$116.60	$116.60
Purchase #4	$28.69	9.201%	$31.3298	$31.33	$31.35	$31.30
Purchase #5	$79.94	12.578%	$89.9949	$89.99	$90.00	$90.00
Purchase #6	$231.88	4.776%	$242.9546	$242.95	$242.95	$243.00
Purchase #7	$37.94	5.511%	$40.0309	$40.03	$40.05	$40.00
7 purchase totals =	$833.19		$882.5784	$882.57	$882.60	$882.50