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	$108.56	8.217%	$117.4804	$117.48	$117.50	$117.50
Purchase #2	$85.81	4.809%	$89.9366	$89.94	$89.95	$89.90
Purchase #3	$234.36	9.568%	$256.7836	$256.78	$256.80	$256.80
Purchase #4	$25.59	7.203%	$27.4332	$27.43	$27.45	$27.40
Purchase #5	$217.79	6.536%	$232.0248	$232.02	$232.00	$232.00
Purchase #6	$12.86	12.440%	$14.4598	$14.46	$14.45	$14.50
Purchase #7	$20.30	5.155%	$21.3465	$21.35	$21.35	$21.30
7 purchase totals =	$705.27		$759.4649	$759.46	$759.50	$759.40