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	$144.64	13.659%	$164.3964	$164.40	$164.40	$164.40
Purchase #2	$64.47	12.700%	$72.6577	$72.66	$72.65	$72.70
Purchase #3	$36.37	8.529%	$39.472	$39.47	$39.45	$39.50
Purchase #4	$81.54	10.341%	$89.9721	$89.97	$89.95	$90.00
Purchase #5	$36.64	3.339%	$37.8634	$37.86	$37.85	$37.90
Purchase #6	$133.70	12.856%	$150.8885	$150.89	$150.90	$150.90
Purchase #7	$190.75	11.293%	$212.2914	$212.29	$212.30	$212.30
7 purchase totals =	$688.11		$767.5415	$767.54	$767.50	$767.70