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	$81.37	6.353%	$86.5394	$86.54	$86.55	$86.50
Purchase #2	$117.25	4.312%	$122.3058	$122.31	$122.30	$122.30
Purchase #3	$50.91	13.600%	$57.8338	$57.83	$57.85	$57.80
Purchase #4	$63.80	11.522%	$71.151	$71.15	$71.15	$71.20
Purchase #5	$68.71	5.528%	$72.5083	$72.51	$72.50	$72.50
Purchase #6	$132.86	6.525%	$141.5291	$141.53	$141.55	$141.50
Purchase #7	$87.77	5.687%	$92.7615	$92.76	$92.75	$92.80
7 purchase totals =	$602.67		$644.6289	$644.63	$644.65	$644.60