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	$29.83	8.186%	$32.2719	$32.27	$32.25	$32.30
Purchase #2	$86.93	12.193%	$97.5294	$97.53	$97.55	$97.50
Purchase #3	$95.33	10.767%	$105.5942	$105.59	$105.60	$105.60
Purchase #4	$45.97	7.803%	$49.557	$49.56	$49.55	$49.60
Purchase #5	$240.46	4.181%	$250.5136	$250.51	$250.50	$250.50
Purchase #6	$33.53	8.197%	$36.2785	$36.28	$36.30	$36.30
Purchase #7	$34.61	8.373%	$37.5079	$37.51	$37.50	$37.50
7 purchase totals =	$566.66		$609.2525	$609.25	$609.25	$609.30