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	$116.83	3.154%	$120.5148	$120.51	$120.50	$120.50
Purchase #2	$200.82	3.742%	$208.3347	$208.33	$208.35	$208.30
Purchase #3	$162.90	3.482%	$168.5722	$168.57	$168.55	$168.60
Purchase #4	$92.94	12.642%	$104.6895	$104.69	$104.70	$104.70
Purchase #5	$177.51	7.557%	$190.9244	$190.92	$190.90	$190.90
Purchase #6	$29.53	10.390%	$32.5982	$32.60	$32.60	$32.60
Purchase #7	$116.61	3.440%	$120.6214	$120.62	$120.60	$120.60
7 purchase totals =	$897.14		$946.2552	$946.24	$946.20	$946.20