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	$131.44	6.251%	$139.6563	$139.66	$139.65	$139.70
Purchase #2	$112.93	10.279%	$124.5381	$124.54	$124.55	$124.50
Purchase #3	$120.36	11.762%	$134.5167	$134.52	$134.50	$134.50
Purchase #4	$81.78	10.131%	$90.0651	$90.07	$90.05	$90.10
Purchase #5	$91.25	7.145%	$97.7698	$97.77	$97.75	$97.80
Purchase #6	$51.74	4.124%	$53.8738	$53.87	$53.85	$53.90
Purchase #7	$137.46	6.589%	$146.5172	$146.52	$146.50	$146.50
7 purchase totals =	$726.96		$786.9370	$786.95	$786.85	$787.00