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	$61.92	12.812%	$69.8532	$69.85	$69.85	$69.90
Purchase #2	$221.97	13.401%	$251.7162	$251.72	$251.70	$251.70
Purchase #3	$199.88	4.380%	$208.6347	$208.63	$208.65	$208.60
Purchase #4	$213.89	11.671%	$238.8531	$238.85	$238.85	$238.90
Purchase #5	$200.33	10.577%	$221.5189	$221.52	$221.50	$221.50
Purchase #6	$171.25	4.422%	$178.8227	$178.82	$178.80	$178.80
Purchase #7	$9.27	12.709%	$10.4481	$10.45	$10.45	$10.40
7 purchase totals =	$1,078.51		$1,179.8469	$1,179.84	$1,179.80	$1,179.80