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	$221.84	4.816%	$232.5238	$232.52	$232.50	$232.50
Purchase #2	$57.60	11.576%	$64.2678	$64.27	$64.25	$64.30
Purchase #3	$177.56	3.127%	$183.1123	$183.11	$183.10	$183.10
Purchase #4	$137.91	7.564%	$148.3415	$148.34	$148.35	$148.30
Purchase #5	$247.29	13.554%	$280.8077	$280.81	$280.80	$280.80
Purchase #6	$34.56	11.654%	$38.5876	$38.59	$38.60	$38.60
Purchase #7	$135.93	11.742%	$151.8909	$151.89	$151.90	$151.90
7 purchase totals =	$1,012.69		$1,099.5316	$1,099.53	$1,099.50	$1,099.50