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 $246.66   6.322%   $262.2538   $262.25   $262.25   $262.30  
  Purchase #2 $190.95   3.295%   $197.2418   $197.24   $197.25   $197.20  
  Purchase #3 $212.46   5.656%   $224.4767   $224.48   $224.50   $224.50  
  Purchase #4 $21.47   5.207%   $22.5879   $22.59   $22.60   $22.60  
  Purchase #5 $19.76   10.241%   $21.7836   $21.78   $21.80   $21.80  
  Purchase #6 $58.56   6.818%   $62.5526   $62.55   $62.55   $62.60  
  Purchase #7 $11.91   12.548%   $13.4045   $13.40   $13.40   $13.40  
  7 purchase totals = $761.77       $804.3009   $804.29   $804.35   $804.40