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	$103.29	9.596%	$113.2017	$113.20	$113.20	$113.20
Purchase #2	$50.95	9.609%	$55.8458	$55.85	$55.85	$55.80
Purchase #3	$151.63	13.349%	$171.8711	$171.87	$171.85	$171.90
Purchase #4	$180.43	9.124%	$196.8924	$196.89	$196.90	$196.90
Purchase #5	$40.48	8.153%	$43.7803	$43.78	$43.80	$43.80
Purchase #6	$58.51	4.283%	$61.016	$61.02	$61.00	$61.00
Purchase #7	$28.31	4.435%	$29.5655	$29.57	$29.55	$29.60
7 purchase totals =	$613.60		$672.1728	$672.18	$672.15	$672.20