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	$11.86	12.843%	$13.3832	$13.38	$13.40	$13.40
Purchase #2	$123.72	13.471%	$140.3863	$140.39	$140.40	$140.40
Purchase #3	$127.73	9.817%	$140.2693	$140.27	$140.25	$140.30
Purchase #4	$244.32	9.650%	$267.8969	$267.90	$267.90	$267.90
Purchase #5	$75.69	10.396%	$83.5587	$83.56	$83.55	$83.60
Purchase #6	$36.67	8.553%	$39.8064	$39.81	$39.80	$39.80
Purchase #7	$107.50	5.782%	$113.7157	$113.72	$113.70	$113.70
7 purchase totals =	$727.49		$799.0165	$799.03	$799.00	$799.10