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	$37.69	5.833%	$39.8885	$39.89	$39.90	$39.90
Purchase #2	$124.86	11.818%	$139.616	$139.62	$139.60	$139.60
Purchase #3	$107.69	8.725%	$117.086	$117.09	$117.10	$117.10
Purchase #4	$64.92	3.841%	$67.4136	$67.41	$67.40	$67.40
Purchase #5	$174.83	12.591%	$196.8428	$196.84	$196.85	$196.80
Purchase #6	$32.25	8.213%	$34.8987	$34.90	$34.90	$34.90
Purchase #7	$143.60	3.456%	$148.5628	$148.56	$148.55	$148.60
7 purchase totals =	$685.84		$744.3084	$744.31	$744.30	$744.30