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	$139.35	6.748%	$148.7533	$148.75	$148.75	$148.80
Purchase #2	$182.83	7.175%	$195.9481	$195.95	$195.95	$195.90
Purchase #3	$51.37	8.638%	$55.8073	$55.81	$55.80	$55.80
Purchase #4	$68.96	13.598%	$78.3372	$78.34	$78.35	$78.30
Purchase #5	$177.83	4.201%	$185.3006	$185.30	$185.30	$185.30
Purchase #6	$232.85	5.587%	$245.8593	$245.86	$245.85	$245.90
Purchase #7	$24.70	4.831%	$25.8933	$25.89	$25.90	$25.90
7 purchase totals =	$877.89		$935.8991	$935.90	$935.90	$935.90