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	$232.93	11.291%	$259.2301	$259.23	$259.25	$259.20
Purchase #2	$129.61	3.830%	$134.5741	$134.57	$134.55	$134.60
Purchase #3	$129.54	9.490%	$141.8333	$141.83	$141.85	$141.80
Purchase #4	$166.67	8.300%	$180.5036	$180.50	$180.50	$180.50
Purchase #5	$40.41	4.725%	$42.3194	$42.32	$42.30	$42.30
Purchase #6	$187.91	4.652%	$196.6516	$196.65	$196.65	$196.70
Purchase #7	$246.54	11.431%	$274.722	$274.72	$274.70	$274.70
7 purchase totals =	$1,133.61		$1,229.8341	$1,229.82	$1,229.80	$1,229.80