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	$45.67	12.562%	$51.4071	$51.41	$51.40	$51.40
Purchase #2	$127.86	8.768%	$139.0708	$139.07	$139.05	$139.10
Purchase #3	$100.46	5.235%	$105.7191	$105.72	$105.70	$105.70
Purchase #4	$105.69	4.592%	$110.5433	$110.54	$110.55	$110.50
Purchase #5	$41.94	8.650%	$45.5678	$45.57	$45.55	$45.60
Purchase #6	$30.34	3.834%	$31.5032	$31.50	$31.50	$31.50
Purchase #7	$181.49	10.194%	$199.9911	$199.99	$200.00	$200.00
7 purchase totals =	$633.45		$683.8024	$683.80	$683.75	$683.80