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	$71.92	12.452%	$80.8755	$80.88	$80.90	$80.90
Purchase #2	$179.34	3.523%	$185.6581	$185.66	$185.65	$185.70
Purchase #3	$69.64	8.469%	$75.5378	$75.54	$75.55	$75.50
Purchase #4	$109.38	3.576%	$113.2914	$113.29	$113.30	$113.30
Purchase #5	$94.56	11.592%	$105.5214	$105.52	$105.50	$105.50
Purchase #6	$238.46	7.309%	$255.889	$255.89	$255.90	$255.90
Purchase #7	$164.32	7.466%	$176.5881	$176.59	$176.60	$176.60
7 purchase totals =	$927.62		$993.3613	$993.37	$993.40	$993.40