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 $79.59   8.656%   $86.4793   $86.48   $86.50   $86.50  
  Purchase #2 $177.92   13.264%   $201.5193   $201.52   $201.50   $201.50  
  Purchase #3 $81.39   13.441%   $92.3296   $92.33   $92.35   $92.30  
  Purchase #4 $240.40   8.817%   $261.5961   $261.60   $261.60   $261.60  
  Purchase #5 $114.56   10.167%   $126.2073   $126.21   $126.20   $126.20  
  Purchase #6 $101.56   7.269%   $108.9424   $108.94   $108.95   $108.90  
  Purchase #7 $203.67   6.792%   $217.5033   $217.50   $217.50   $217.50  
  7 purchase totals = $999.09       $1,094.5773   $1,094.58   $1,094.60   $1,094.50