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	$19.70	3.570%	$20.4033	$20.40	$20.40	$20.40
Purchase #2	$209.67	10.490%	$231.6644	$231.66	$231.65	$231.70
Purchase #3	$120.87	13.681%	$137.4062	$137.41	$137.40	$137.40
Purchase #4	$195.96	11.808%	$219.099	$219.10	$219.10	$219.10
Purchase #5	$240.48	13.263%	$272.3749	$272.37	$272.35	$272.40
Purchase #6	$43.50	11.454%	$48.4825	$48.48	$48.50	$48.50
Purchase #7	$72.61	8.239%	$78.5923	$78.59	$78.60	$78.60
7 purchase totals =	$902.79		$1,008.0226	$1,008.01	$1,008.00	$1,008.10