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	$109.47	6.580%	$116.6731	$116.67	$116.65	$116.70
Purchase #2	$229.95	7.822%	$247.9367	$247.94	$247.95	$247.90
Purchase #3	$206.82	8.851%	$225.1256	$225.13	$225.15	$225.10
Purchase #4	$108.36	12.598%	$122.0112	$122.01	$122.00	$122.00
Purchase #5	$76.48	3.127%	$78.8715	$78.87	$78.85	$78.90
Purchase #6	$133.63	4.705%	$139.9173	$139.92	$139.90	$139.90
Purchase #7	$90.96	4.247%	$94.8231	$94.82	$94.80	$94.80
7 purchase totals =	$955.67		$1,025.3585	$1,025.36	$1,025.30	$1,025.30