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 $52.31   7.118%   $56.0334   $56.03   $56.05   $56.00  
  Purchase #2 $202.27   11.238%   $225.0011   $225.00   $225.00   $225.00  
  Purchase #3 $109.73   12.682%   $123.646   $123.65   $123.65   $123.60  
  Purchase #4 $38.70   5.767%   $40.9318   $40.93   $40.95   $40.90  
  Purchase #5 $173.37   6.279%   $184.2559   $184.26   $184.25   $184.30  
  Purchase #6 $63.60   6.477%   $67.7194   $67.72   $67.70   $67.70  
  Purchase #7 $225.36   11.354%   $250.9474   $250.95   $250.95   $250.90  
  7 purchase totals = $865.34       $948.5350   $948.54   $948.55   $948.40