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 $65.59   11.811%   $73.3368   $73.34   $73.35   $73.30  
  Purchase #2 $238.41   8.296%   $258.1885   $258.19   $258.20   $258.20  
  Purchase #3 $144.62   5.597%   $152.7144   $152.71   $152.70   $152.70  
  Purchase #4 $47.72   12.434%   $53.6535   $53.65   $53.65   $53.70  
  Purchase #5 $236.41   12.821%   $266.7201   $266.72   $266.70   $266.70  
  Purchase #6 $128.81   7.383%   $138.32   $138.32   $138.30   $138.30  
  Purchase #7 $52.75   5.455%   $55.6275   $55.63   $55.65   $55.60  
  7 purchase totals = $914.31       $998.5608   $998.56   $998.55   $998.50