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	$37.63	8.233%	$40.7281	$40.73	$40.75	$40.70
Purchase #2	$61.31	10.812%	$67.9388	$67.94	$67.95	$67.90
Purchase #3	$201.43	10.717%	$223.0173	$223.02	$223.00	$223.00
Purchase #4	$178.47	6.335%	$189.7761	$189.78	$189.80	$189.80
Purchase #5	$100.56	13.411%	$114.0461	$114.05	$114.05	$114.00
Purchase #6	$148.85	10.394%	$164.3215	$164.32	$164.30	$164.30
Purchase #7	$20.85	10.350%	$23.008	$23.01	$23.00	$23.00
7 purchase totals =	$749.10		$822.8359	$822.85	$822.85	$822.70