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	$90.73	4.142%	$94.488	$94.49	$94.50	$94.50
Purchase #2	$179.66	10.793%	$199.0507	$199.05	$199.05	$199.10
Purchase #3	$138.51	12.430%	$155.7268	$155.73	$155.75	$155.70
Purchase #4	$13.83	5.388%	$14.5752	$14.58	$14.60	$14.60
Purchase #5	$18.91	10.408%	$20.8782	$20.88	$20.90	$20.90
Purchase #6	$162.73	11.767%	$181.8784	$181.88	$181.90	$181.90
Purchase #7	$236.48	12.167%	$265.2525	$265.25	$265.25	$265.30
7 purchase totals =	$840.85		$931.8498	$931.86	$931.95	$932.00