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 $93.73   11.706%   $104.702   $104.70   $104.70   $104.70  
  Purchase #2 $169.63   11.716%   $189.5039   $189.50   $189.50   $189.50  
  Purchase #3 $202.29   13.102%   $228.794   $228.79   $228.80   $228.80  
  Purchase #4 $43.75   13.603%   $49.7013   $49.70   $49.70   $49.70  
  Purchase #5 $164.87   6.515%   $175.6113   $175.61   $175.60   $175.60  
  Purchase #6 $236.26   13.443%   $268.0204   $268.02   $268.00   $268.00  
  Purchase #7 $71.31   7.851%   $76.9085   $76.91   $76.90   $76.90  
  7 purchase totals = $981.84       $1,093.2414   $1,093.23   $1,093.20   $1,093.20