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	$240.61	6.696%	$256.7212	$256.72	$256.70	$256.70
Purchase #2	$86.69	4.501%	$90.5919	$90.59	$90.60	$90.60
Purchase #3	$126.75	6.833%	$135.4108	$135.41	$135.40	$135.40
Purchase #4	$131.54	3.745%	$136.4662	$136.47	$136.45	$136.50
Purchase #5	$87.83	12.175%	$98.5233	$98.52	$98.50	$98.50
Purchase #6	$92.86	3.437%	$96.0516	$96.05	$96.05	$96.10
Purchase #7	$130.49	4.323%	$136.1311	$136.13	$136.15	$136.10
7 purchase totals =	$896.77		$949.8961	$949.89	$949.85	$949.90