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	$59.47	6.820%	$63.5259	$63.53	$63.55	$63.50
Purchase #2	$136.51	3.209%	$140.8906	$140.89	$140.90	$140.90
Purchase #3	$86.36	4.333%	$90.102	$90.10	$90.10	$90.10
Purchase #4	$160.86	8.314%	$174.2339	$174.23	$174.25	$174.20
Purchase #5	$6.45	5.542%	$6.8075	$6.81	$6.80	$6.80
Purchase #6	$103.55	10.227%	$114.1401	$114.14	$114.15	$114.10
Purchase #7	$56.63	4.630%	$59.252	$59.25	$59.25	$59.30
7 purchase totals =	$609.83		$648.9520	$648.95	$649.00	$648.90