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	$82.40	5.814%	$87.1907	$87.19	$87.20	$87.20
Purchase #2	$30.54	10.781%	$33.8325	$33.83	$33.85	$33.80
Purchase #3	$113.88	10.706%	$126.072	$126.07	$126.05	$126.10
Purchase #4	$172.78	6.695%	$184.3476	$184.35	$184.35	$184.30
Purchase #5	$89.74	5.286%	$94.4837	$94.48	$94.50	$94.50
Purchase #6	$64.42	3.105%	$66.4202	$66.42	$66.40	$66.40
Purchase #7	$66.35	9.556%	$72.6904	$72.69	$72.70	$72.70
7 purchase totals =	$620.11		$665.0371	$665.03	$665.05	$665.00