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 $232.37   12.749%   $261.9949   $261.99   $262.00   $262.00  
  Purchase #2 $70.53   11.227%   $78.4484   $78.45   $78.45   $78.40  
  Purchase #3 $228.82   6.207%   $243.0229   $243.02   $243.00   $243.00  
  Purchase #4 $181.92   6.365%   $193.4992   $193.50   $193.50   $193.50  
  Purchase #5 $189.49   12.563%   $213.2956   $213.30   $213.30   $213.30  
  Purchase #6 $54.69   9.268%   $59.7587   $59.76   $59.75   $59.80  
  Purchase #7 $71.70   3.139%   $73.9507   $73.95   $73.95   $74.00  
  7 purchase totals = $1,029.52       $1,123.9704   $1,123.97   $1,123.95   $1,124.00