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	$129.57	7.735%	$139.5922	$139.59	$139.60	$139.60
Purchase #2	$118.90	11.799%	$132.929	$132.93	$132.95	$132.90
Purchase #3	$20.64	6.199%	$21.9195	$21.92	$21.90	$21.90
Purchase #4	$97.26	12.654%	$109.5673	$109.57	$109.55	$109.60
Purchase #5	$40.73	9.387%	$44.5533	$44.55	$44.55	$44.60
Purchase #6	$181.48	3.206%	$187.2982	$187.30	$187.30	$187.30
Purchase #7	$214.43	4.274%	$223.5947	$223.59	$223.60	$223.60
7 purchase totals =	$803.01		$859.4542	$859.45	$859.45	$859.50