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	$80.44	3.289%	$83.0857	$83.09	$83.10	$83.10
Purchase #2	$82.86	7.620%	$89.1739	$89.17	$89.15	$89.20
Purchase #3	$108.82	8.682%	$118.2678	$118.27	$118.25	$118.30
Purchase #4	$70.66	11.149%	$78.5379	$78.54	$78.55	$78.50
Purchase #5	$250.28	9.475%	$273.994	$273.99	$274.00	$274.00
Purchase #6	$84.27	13.178%	$95.3751	$95.38	$95.40	$95.40
Purchase #7	$140.30	7.559%	$150.9053	$150.91	$150.90	$150.90
7 purchase totals =	$817.63		$889.3397	$889.35	$889.35	$889.40