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	$116.70	4.329%	$121.7519	$121.75	$121.75	$121.80
Purchase #2	$65.33	9.334%	$71.4279	$71.43	$71.45	$71.40
Purchase #3	$139.29	3.255%	$143.8239	$143.82	$143.80	$143.80
Purchase #4	$121.76	8.328%	$131.9002	$131.90	$131.90	$131.90
Purchase #5	$32.39	13.758%	$36.8462	$36.85	$36.85	$36.80
Purchase #6	$90.64	13.167%	$102.5746	$102.57	$102.55	$102.60
Purchase #7	$242.43	12.405%	$272.5034	$272.50	$272.50	$272.50
7 purchase totals =	$808.54		$880.8281	$880.82	$880.80	$880.80