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 $54.38   6.560%   $57.9473   $57.95   $57.95   $57.90  
  Purchase #2 $23.79   11.375%   $26.4961   $26.50   $26.50   $26.50  
  Purchase #3 $160.27   9.164%   $174.9571   $174.96   $174.95   $175.00  
  Purchase #4 $68.81   11.616%   $76.803   $76.80   $76.80   $76.80  
  Purchase #5 $69.99   3.456%   $72.4089   $72.41   $72.40   $72.40  
  Purchase #6 $128.71   13.438%   $146.006   $146.01   $146.00   $146.00  
  Purchase #7 $243.25   7.655%   $261.8708   $261.87   $261.85   $261.90  
  7 purchase totals = $749.20       $816.4892   $816.50   $816.45   $816.50