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 $58.77   9.347%   $64.2632   $64.26   $64.25   $64.30  
  Purchase #2 $211.58   8.217%   $228.9655   $228.97   $228.95   $229.00  
  Purchase #3 $106.87   11.229%   $118.8704   $118.87   $118.85   $118.90  
  Purchase #4 $45.92   13.380%   $52.0641   $52.06   $52.05   $52.10  
  Purchase #5 $137.29   8.313%   $148.7029   $148.70   $148.70   $148.70  
  Purchase #6 $182.29   6.825%   $194.7313   $194.73   $194.75   $194.70  
  Purchase #7 $155.87   5.523%   $164.4787   $164.48   $164.50   $164.50  
  7 purchase totals = $898.59       $972.0761   $972.07   $972.05   $972.20