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 $134.48   9.162%   $146.8011   $146.80   $146.80   $146.80  
  Purchase #2 $143.87   9.540%   $157.5952   $157.60   $157.60   $157.60  
  Purchase #3 $243.71   7.146%   $261.1255   $261.13   $261.15   $261.10  
  Purchase #4 $207.93   13.369%   $235.7282   $235.73   $235.75   $235.70  
  Purchase #5 $194.75   6.755%   $207.9054   $207.91   $207.90   $207.90  
  Purchase #6 $148.79   10.705%   $164.718   $164.72   $164.70   $164.70  
  Purchase #7 $77.83   6.378%   $82.794   $82.79   $82.80   $82.80  
  7 purchase totals = $1,151.36       $1,256.6674   $1,256.68   $1,256.70   $1,256.60