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	$35.73	8.670%	$38.8278	$38.83	$38.85	$38.80
Purchase #2	$130.78	8.438%	$141.8152	$141.82	$141.80	$141.80
Purchase #3	$168.64	4.706%	$176.5762	$176.58	$176.60	$176.60
Purchase #4	$143.34	7.110%	$153.5315	$153.53	$153.55	$153.50
Purchase #5	$46.48	13.483%	$52.7469	$52.75	$52.75	$52.70
Purchase #6	$35.64	4.137%	$37.1144	$37.11	$37.10	$37.10
Purchase #7	$131.66	10.798%	$145.8766	$145.88	$145.90	$145.90
7 purchase totals =	$692.27		$746.4886	$746.50	$746.55	$746.40