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	$78.43	9.214%	$85.6565	$85.66	$85.65	$85.70
Purchase #2	$164.35	12.854%	$185.4755	$185.48	$185.50	$185.50
Purchase #3	$11.29	13.725%	$12.8396	$12.84	$12.85	$12.80
Purchase #4	$228.87	6.579%	$243.9274	$243.93	$243.95	$243.90
Purchase #5	$116.67	12.567%	$131.3319	$131.33	$131.35	$131.30
Purchase #6	$75.32	6.240%	$80.02	$80.02	$80.00	$80.00
Purchase #7	$83.84	8.185%	$90.7023	$90.70	$90.70	$90.70
7 purchase totals =	$758.77		$829.9532	$829.96	$830.00	$829.90