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 $99.80   13.292%   $113.0654   $113.07   $113.05   $113.10  
  Purchase #2 $60.53   7.484%   $65.0601   $65.06   $65.05   $65.10  
  Purchase #3 $6.63   12.713%   $7.4729   $7.47   $7.45   $7.50  
  Purchase #4 $247.82   5.644%   $261.807   $261.81   $261.80   $261.80  
  Purchase #5 $85.86   9.696%   $94.185   $94.19   $94.20   $94.20  
  Purchase #6 $246.99   7.702%   $266.0132   $266.01   $266.00   $266.00  
  Purchase #7 $250.77   11.362%   $279.2625   $279.26   $279.25   $279.30  
  7 purchase totals = $998.40       $1,086.8661   $1,086.87   $1,086.80   $1,087.00