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	$7.84	11.248%	$8.7218	$8.72	$8.70	$8.70
Purchase #2	$122.93	9.802%	$134.9796	$134.98	$135.00	$135.00
Purchase #3	$105.87	5.287%	$111.4673	$111.47	$111.45	$111.50
Purchase #4	$207.66	10.293%	$229.0344	$229.03	$229.05	$229.00
Purchase #5	$40.56	5.464%	$42.7762	$42.78	$42.80	$42.80
Purchase #6	$202.79	6.260%	$215.4847	$215.48	$215.50	$215.50
Purchase #7	$150.72	5.104%	$158.4127	$158.41	$158.40	$158.40
7 purchase totals =	$838.37		$900.8767	$900.87	$900.90	$900.90