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	$232.51	12.849%	$262.3852	$262.39	$262.40	$262.40
Purchase #2	$12.30	8.867%	$13.3906	$13.39	$13.40	$13.40
Purchase #3	$103.66	7.313%	$111.2407	$111.24	$111.25	$111.20
Purchase #4	$191.53	4.361%	$199.8826	$199.88	$199.90	$199.90
Purchase #5	$50.59	4.590%	$52.9121	$52.91	$52.90	$52.90
Purchase #6	$246.85	4.696%	$258.4421	$258.44	$258.45	$258.40
Purchase #7	$92.47	5.798%	$97.8314	$97.83	$97.85	$97.80
7 purchase totals =	$929.91		$996.0847	$996.08	$996.15	$996.00