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	$216.66	6.665%	$231.1004	$231.10	$231.10	$231.10
Purchase #2	$246.46	3.235%	$254.433	$254.43	$254.45	$254.40
Purchase #3	$201.55	10.292%	$222.2935	$222.29	$222.30	$222.30
Purchase #4	$180.89	8.705%	$196.6365	$196.64	$196.65	$196.60
Purchase #5	$116.89	11.128%	$129.8975	$129.90	$129.90	$129.90
Purchase #6	$17.97	5.513%	$18.9607	$18.96	$18.95	$19.00
Purchase #7	$31.67	6.144%	$33.6158	$33.62	$33.60	$33.60
7 purchase totals =	$1,012.09		$1,086.9374	$1,086.94	$1,086.95	$1,086.90