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	$67.29	3.871%	$69.8948	$69.89	$69.90	$69.90
Purchase #2	$218.71	11.349%	$243.5314	$243.53	$243.55	$243.50
Purchase #3	$63.94	5.517%	$67.4676	$67.47	$67.45	$67.50
Purchase #4	$222.66	7.531%	$239.4285	$239.43	$239.45	$239.40
Purchase #5	$63.33	4.121%	$65.9398	$65.94	$65.95	$65.90
Purchase #6	$217.38	13.189%	$246.0502	$246.05	$246.05	$246.10
Purchase #7	$39.52	3.582%	$40.9356	$40.94	$40.95	$40.90
7 purchase totals =	$892.83		$973.2479	$973.25	$973.30	$973.20