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	$32.46	3.868%	$33.7156	$33.72	$33.70	$33.70
Purchase #2	$188.85	4.414%	$197.1858	$197.19	$197.20	$197.20
Purchase #3	$108.48	3.682%	$112.4742	$112.47	$112.45	$112.50
Purchase #4	$162.47	3.795%	$168.6357	$168.64	$168.65	$168.60
Purchase #5	$60.34	12.412%	$67.8294	$67.83	$67.85	$67.80
Purchase #6	$243.31	8.604%	$264.2444	$264.24	$264.25	$264.20
Purchase #7	$217.57	9.177%	$237.5364	$237.54	$237.55	$237.50
7 purchase totals =	$1,013.48		$1,081.6215	$1,081.63	$1,081.65	$1,081.50