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 $59.26   11.834%   $66.2728   $66.27   $66.25   $66.30  
  Purchase #2 $111.69   8.811%   $121.531   $121.53   $121.55   $121.50  
  Purchase #3 $158.87   9.808%   $174.452   $174.45   $174.45   $174.50  
  Purchase #4 $15.54   13.850%   $17.6923   $17.69   $17.70   $17.70  
  Purchase #5 $121.40   3.604%   $125.7753   $125.78   $125.80   $125.80  
  Purchase #6 $66.25   8.328%   $71.7673   $71.77   $71.75   $71.80  
  Purchase #7 $177.52   7.626%   $191.0577   $191.06   $191.05   $191.10  
  7 purchase totals = $710.53       $768.5484   $768.55   $768.55   $768.70