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 $49.87   13.167%   $56.4364   $56.44   $56.45   $56.40  
  Purchase #2 $7.34   4.763%   $7.6896   $7.69   $7.70   $7.70  
  Purchase #3 $95.41   9.704%   $104.6686   $104.67   $104.65   $104.70  
  Purchase #4 $208.39   7.485%   $223.988   $223.99   $224.00   $224.00  
  Purchase #5 $180.79   5.120%   $190.0464   $190.05   $190.05   $190.00  
  Purchase #6 $170.39   6.601%   $181.6374   $181.64   $181.65   $181.60  
  Purchase #7 $97.62   5.122%   $102.6201   $102.62   $102.60   $102.60  
  7 purchase totals = $809.81       $867.0865   $867.10   $867.10   $867.00