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	$11.62	7.682%	$12.5126	$12.51	$12.50	$12.50
Purchase #2	$171.74	4.460%	$179.3996	$179.40	$179.40	$179.40
Purchase #3	$125.65	8.318%	$136.1016	$136.10	$136.10	$136.10
Purchase #4	$128.97	10.103%	$141.9998	$142.00	$142.00	$142.00
Purchase #5	$88.31	12.684%	$99.5112	$99.51	$99.50	$99.50
Purchase #6	$146.68	6.611%	$156.377	$156.38	$156.40	$156.40
Purchase #7	$69.40	6.751%	$74.0852	$74.09	$74.10	$74.10
7 purchase totals =	$742.37		$799.9870	$799.99	$800.00	$800.00