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 $57.41   10.493%   $63.434   $63.43   $63.45   $63.40  
  Purchase #2 $30.46   13.861%   $34.6821   $34.68   $34.70   $34.70  
  Purchase #3 $34.65   8.679%   $37.6573   $37.66   $37.65   $37.70  
  Purchase #4 $59.72   3.714%   $61.938   $61.94   $61.95   $61.90  
  Purchase #5 $142.77   4.732%   $149.5259   $149.53   $149.55   $149.50  
  Purchase #6 $232.83   7.127%   $249.4238   $249.42   $249.40   $249.40  
  Purchase #7 $25.25   3.479%   $26.1284   $26.13   $26.15   $26.10  
  7 purchase totals = $583.09       $622.7895   $622.79   $622.85   $622.70