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	$20.65	4.143%	$21.5055	$21.51	$21.50	$21.50
Purchase #2	$40.71	7.563%	$43.7889	$43.79	$43.80	$43.80
Purchase #3	$53.27	12.428%	$59.8904	$59.89	$59.90	$59.90
Purchase #4	$123.52	10.342%	$136.2944	$136.29	$136.30	$136.30
Purchase #5	$14.80	10.814%	$16.4005	$16.40	$16.40	$16.40
Purchase #6	$13.34	7.108%	$14.2882	$14.29	$14.30	$14.30
Purchase #7	$205.56	9.154%	$224.377	$224.38	$224.40	$224.40
7 purchase totals =	$471.85		$516.5449	$516.55	$516.60	$516.60