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	$77.79	9.661%	$85.3053	$85.31	$85.30	$85.30
Purchase #2	$163.57	3.429%	$169.1788	$169.18	$169.20	$169.20
Purchase #3	$103.91	9.567%	$113.8511	$113.85	$113.85	$113.90
Purchase #4	$38.59	9.458%	$42.2398	$42.24	$42.25	$42.20
Purchase #5	$51.53	11.612%	$57.5137	$57.51	$57.50	$57.50
Purchase #6	$65.90	10.721%	$72.9651	$72.97	$72.95	$73.00
Purchase #7	$90.34	13.122%	$102.1944	$102.19	$102.20	$102.20
7 purchase totals =	$591.63		$643.2482	$643.25	$643.25	$643.30