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	$73.48	11.840%	$82.18	$82.18	$82.20	$82.20
Purchase #2	$116.79	12.645%	$131.5581	$131.56	$131.55	$131.60
Purchase #3	$153.50	9.376%	$167.8922	$167.89	$167.90	$167.90
Purchase #4	$78.76	5.405%	$83.017	$83.02	$83.00	$83.00
Purchase #5	$66.58	8.414%	$72.182	$72.18	$72.20	$72.20
Purchase #6	$116.93	3.354%	$120.8518	$120.85	$120.85	$120.90
Purchase #7	$96.85	12.421%	$108.8797	$108.88	$108.90	$108.90
7 purchase totals =	$702.89		$766.5608	$766.56	$766.60	$766.70