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	$129.53	12.438%	$145.6409	$145.64	$145.65	$145.60
Purchase #2	$162.31	10.697%	$179.6723	$179.67	$179.65	$179.70
Purchase #3	$94.78	6.617%	$101.0516	$101.05	$101.05	$101.10
Purchase #4	$7.89	12.746%	$8.8957	$8.90	$8.90	$8.90
Purchase #5	$156.64	10.128%	$172.5045	$172.50	$172.50	$172.50
Purchase #6	$74.44	5.678%	$78.6667	$78.67	$78.65	$78.70
Purchase #7	$37.99	13.318%	$43.0495	$43.05	$43.05	$43.00
7 purchase totals =	$663.58		$729.4812	$729.48	$729.45	$729.50