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	$84.60	7.396%	$90.857	$90.86	$90.85	$90.90
Purchase #2	$123.80	4.701%	$129.6198	$129.62	$129.60	$129.60
Purchase #3	$196.50	4.277%	$204.9043	$204.90	$204.90	$204.90
Purchase #4	$183.77	13.374%	$208.3474	$208.35	$208.35	$208.30
Purchase #5	$31.47	7.682%	$33.8875	$33.89	$33.90	$33.90
Purchase #6	$87.86	8.183%	$95.0496	$95.05	$95.05	$95.00
Purchase #7	$81.48	7.823%	$87.8542	$87.85	$87.85	$87.90
7 purchase totals =	$789.48		$850.5198	$850.52	$850.50	$850.50