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	$39.30	4.186%	$40.9451	$40.95	$40.95	$40.90
Purchase #2	$164.94	13.650%	$187.4543	$187.45	$187.45	$187.50
Purchase #3	$154.37	13.170%	$174.7005	$174.70	$174.70	$174.70
Purchase #4	$139.43	12.290%	$156.5659	$156.57	$156.55	$156.60
Purchase #5	$40.60	3.443%	$41.9979	$42.00	$42.00	$42.00
Purchase #6	$120.38	3.673%	$124.8016	$124.80	$124.80	$124.80
Purchase #7	$136.62	13.508%	$155.0746	$155.07	$155.05	$155.10
7 purchase totals =	$795.64		$881.5399	$881.54	$881.50	$881.60