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	$72.72	8.477%	$78.8845	$78.88	$78.90	$78.90
Purchase #2	$207.67	12.216%	$233.039	$233.04	$233.05	$233.00
Purchase #3	$143.40	3.445%	$148.3401	$148.34	$148.35	$148.30
Purchase #4	$113.25	4.275%	$118.0914	$118.09	$118.10	$118.10
Purchase #5	$120.94	6.684%	$129.0236	$129.02	$129.00	$129.00
Purchase #6	$37.90	11.761%	$42.3574	$42.36	$42.35	$42.40
Purchase #7	$40.75	6.235%	$43.2908	$43.29	$43.30	$43.30
7 purchase totals =	$736.63		$793.0268	$793.02	$793.05	$793.00