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 $95.60   7.354%   $102.6304   $102.63   $102.65   $102.60  
  Purchase #2 $235.55   11.112%   $261.7243   $261.72   $261.70   $261.70  
  Purchase #3 $32.29   7.292%   $34.6446   $34.64   $34.65   $34.60  
  Purchase #4 $168.52   3.791%   $174.9086   $174.91   $174.90   $174.90  
  Purchase #5 $116.53   6.432%   $124.0252   $124.03   $124.05   $124.00  
  Purchase #6 $217.40   8.345%   $235.542   $235.54   $235.55   $235.50  
  Purchase #7 $111.90   10.571%   $123.7289   $123.73   $123.75   $123.70  
  7 purchase totals = $977.79       $1,057.2040   $1,057.20   $1,057.25   $1,057.00