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	$19.83	9.319%	$21.678	$21.68	$21.70	$21.70
Purchase #2	$158.76	3.516%	$164.342	$164.34	$164.35	$164.30
Purchase #3	$197.70	9.219%	$215.926	$215.93	$215.95	$215.90
Purchase #4	$208.30	3.449%	$215.4843	$215.48	$215.50	$215.50
Purchase #5	$69.46	4.394%	$72.5121	$72.51	$72.50	$72.50
Purchase #6	$33.93	12.126%	$38.0444	$38.04	$38.05	$38.00
Purchase #7	$79.62	9.801%	$87.4236	$87.42	$87.40	$87.40
7 purchase totals =	$767.60		$815.4104	$815.40	$815.45	$815.30