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 $174.77   13.874%   $199.0176   $199.02   $199.00   $199.00  
  Purchase #2 $107.77   13.538%   $122.3599   $122.36   $122.35   $122.40  
  Purchase #3 $217.93   8.274%   $235.9615   $235.96   $235.95   $236.00  
  Purchase #4 $121.62   9.200%   $132.809   $132.81   $132.80   $132.80  
  Purchase #5 $189.80   13.371%   $215.1782   $215.18   $215.20   $215.20  
  Purchase #6 $179.35   4.742%   $187.8548   $187.85   $187.85   $187.90  
  Purchase #7 $241.69   8.253%   $261.6367   $261.64   $261.65   $261.60  
  7 purchase totals = $1,232.93       $1,354.8177   $1,354.82   $1,354.80   $1,354.90