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	$58.71	10.516%	$64.8839	$64.88	$64.90	$64.90
Purchase #2	$224.73	8.527%	$243.8927	$243.89	$243.90	$243.90
Purchase #3	$27.89	12.799%	$31.4596	$31.46	$31.45	$31.50
Purchase #4	$109.53	8.602%	$118.9518	$118.95	$118.95	$119.00
Purchase #5	$85.80	4.240%	$89.4379	$89.44	$89.45	$89.40
Purchase #6	$151.34	3.407%	$156.4962	$156.50	$156.50	$156.50
Purchase #7	$98.57	3.553%	$102.0722	$102.07	$102.05	$102.10
7 purchase totals =	$756.57		$807.1943	$807.19	$807.20	$807.30