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	$229.96	8.665%	$249.886	$249.89	$249.90	$249.90
Purchase #2	$124.71	13.728%	$141.8302	$141.83	$141.85	$141.80
Purchase #3	$157.57	11.614%	$175.8702	$175.87	$175.85	$175.90
Purchase #4	$29.52	12.779%	$33.2924	$33.29	$33.30	$33.30
Purchase #5	$224.82	10.757%	$249.0039	$249.00	$249.00	$249.00
Purchase #6	$190.77	9.308%	$208.5269	$208.53	$208.55	$208.50
Purchase #7	$250.59	11.866%	$280.325	$280.33	$280.35	$280.30
7 purchase totals =	$1,207.94		$1,338.7346	$1,338.74	$1,338.80	$1,338.70