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 $91.76   5.387%   $96.7031   $96.70   $96.70   $96.70  
  Purchase #2 $10.49   12.751%   $11.8276   $11.83   $11.85   $11.80  
  Purchase #3 $218.66   8.590%   $237.4429   $237.44   $237.45   $237.40  
  Purchase #4 $54.66   9.110%   $59.6395   $59.64   $59.65   $59.60  
  Purchase #5 $161.88   12.504%   $182.1215   $182.12   $182.10   $182.10  
  Purchase #6 $63.25   6.657%   $67.4606   $67.46   $67.45   $67.50  
  Purchase #7 $76.30   8.226%   $82.5764   $82.58   $82.60   $82.60  
  7 purchase totals = $677.00       $737.7716   $737.77   $737.80   $737.70