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	$93.92	6.786%	$100.2934	$100.29	$100.30	$100.30
Purchase #2	$137.53	9.349%	$150.3877	$150.39	$150.40	$150.40
Purchase #3	$72.70	5.400%	$76.6258	$76.63	$76.65	$76.60
Purchase #4	$31.34	5.294%	$32.9991	$33.00	$33.00	$33.00
Purchase #5	$141.90	3.182%	$146.4153	$146.42	$146.40	$146.40
Purchase #6	$108.67	3.517%	$112.4919	$112.49	$112.50	$112.50
Purchase #7	$150.35	6.442%	$160.0355	$160.04	$160.05	$160.00
7 purchase totals =	$736.41		$779.2487	$779.26	$779.30	$779.20