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	$154.96	6.762%	$165.4384	$165.44	$165.45	$165.40
Purchase #2	$36.64	9.625%	$40.1666	$40.17	$40.15	$40.20
Purchase #3	$40.47	6.129%	$42.9504	$42.95	$42.95	$43.00
Purchase #4	$136.68	5.535%	$144.2452	$144.25	$144.25	$144.20
Purchase #5	$68.88	4.542%	$72.0085	$72.01	$72.00	$72.00
Purchase #6	$131.64	9.257%	$143.8259	$143.83	$143.85	$143.80
Purchase #7	$80.37	12.677%	$90.5585	$90.56	$90.55	$90.60
7 purchase totals =	$649.64		$699.1935	$699.21	$699.20	$699.20