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 $151.27   8.298%   $163.8224   $163.82   $163.80   $163.80  
  Purchase #2 $59.58   11.752%   $66.5818   $66.58   $66.60   $66.60  
  Purchase #3 $192.46   3.355%   $198.917   $198.92   $198.90   $198.90  
  Purchase #4 $82.93   12.788%   $93.5351   $93.54   $93.55   $93.50  
  Purchase #5 $61.66   5.850%   $65.2671   $65.27   $65.25   $65.30  
  Purchase #6 $126.45   13.236%   $143.1869   $143.19   $143.20   $143.20  
  Purchase #7 $196.47   8.443%   $213.058   $213.06   $213.05   $213.10  
  7 purchase totals = $870.82       $944.3683   $944.38   $944.35   $944.40