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 $56.55   8.286%   $61.2357   $61.24   $61.25   $61.20  
  Purchase #2 $52.72   12.204%   $59.1539   $59.15   $59.15   $59.20  
  Purchase #3 $73.66   6.754%   $78.635   $78.64   $78.65   $78.60  
  Purchase #4 $154.86   9.174%   $169.0669   $169.07   $169.05   $169.10  
  Purchase #5 $182.43   11.526%   $203.4569   $203.46   $203.45   $203.50  
  Purchase #6 $243.46   7.352%   $261.3592   $261.36   $261.35   $261.40  
  Purchase #7 $186.38   12.775%   $210.19   $210.19   $210.20   $210.20  
  7 purchase totals = $950.06       $1,043.0976   $1,043.11   $1,043.10   $1,043.20