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	$236.63	8.218%	$256.0763	$256.08	$256.10	$256.10
Purchase #2	$10.40	6.736%	$11.1005	$11.10	$11.10	$11.10
Purchase #3	$99.89	8.158%	$108.039	$108.04	$108.05	$108.00
Purchase #4	$12.59	9.470%	$13.7823	$13.78	$13.80	$13.80
Purchase #5	$131.92	5.729%	$139.4777	$139.48	$139.50	$139.50
Purchase #6	$141.30	11.325%	$157.3022	$157.30	$157.30	$157.30
Purchase #7	$158.43	8.320%	$171.6114	$171.61	$171.60	$171.60
7 purchase totals =	$791.16		$857.3894	$857.39	$857.45	$857.40