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	$131.31	12.425%	$147.6253	$147.63	$147.65	$147.60
Purchase #2	$182.43	9.509%	$199.7773	$199.78	$199.80	$199.80
Purchase #3	$219.66	13.377%	$249.0439	$249.04	$249.05	$249.00
Purchase #4	$18.33	6.155%	$19.4582	$19.46	$19.45	$19.50
Purchase #5	$116.85	5.659%	$123.4625	$123.46	$123.45	$123.50
Purchase #6	$155.59	8.383%	$168.6331	$168.63	$168.65	$168.60
Purchase #7	$108.47	11.225%	$120.6458	$120.65	$120.65	$120.60
7 purchase totals =	$932.64		$1,028.6461	$1,028.65	$1,028.70	$1,028.60