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	$18.78	11.351%	$20.9117	$20.91	$20.90	$20.90
Purchase #2	$220.35	10.741%	$244.0178	$244.02	$244.00	$244.00
Purchase #3	$145.54	3.241%	$150.257	$150.26	$150.25	$150.30
Purchase #4	$117.51	12.227%	$131.8779	$131.88	$131.90	$131.90
Purchase #5	$202.69	8.458%	$219.8335	$219.83	$219.85	$219.80
Purchase #6	$203.87	10.610%	$225.5006	$225.50	$225.50	$225.50
Purchase #7	$57.86	9.151%	$63.1548	$63.15	$63.15	$63.20
7 purchase totals =	$966.60		$1,055.5533	$1,055.55	$1,055.55	$1,055.60