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	$55.80	13.504%	$63.3352	$63.34	$63.35	$63.30
Purchase #2	$243.73	12.676%	$274.6252	$274.63	$274.65	$274.60
Purchase #3	$24.43	4.308%	$25.4824	$25.48	$25.50	$25.50
Purchase #4	$126.43	8.732%	$137.4699	$137.47	$137.45	$137.50
Purchase #5	$71.95	9.619%	$78.8709	$78.87	$78.85	$78.90
Purchase #6	$196.48	10.817%	$217.7332	$217.73	$217.75	$217.70
Purchase #7	$165.29	8.280%	$178.976	$178.98	$179.00	$179.00
7 purchase totals =	$884.11		$976.4928	$976.50	$976.55	$976.50