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	$131.90	3.628%	$136.6853	$136.69	$136.70	$136.70
Purchase #2	$85.85	13.323%	$97.2878	$97.29	$97.30	$97.30
Purchase #3	$118.83	11.377%	$132.3493	$132.35	$132.35	$132.30
Purchase #4	$95.54	5.538%	$100.831	$100.83	$100.85	$100.80
Purchase #5	$142.59	7.566%	$153.3784	$153.38	$153.40	$153.40
Purchase #6	$217.59	13.328%	$246.5904	$246.59	$246.60	$246.60
Purchase #7	$182.67	9.316%	$199.6875	$199.69	$199.70	$199.70
7 purchase totals =	$974.97		$1,066.8097	$1,066.82	$1,066.90	$1,066.80