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 $61.46   13.339%   $69.6581   $69.66   $69.65   $69.70  
  Purchase #2 $68.40   12.826%   $77.173   $77.17   $77.15   $77.20  
  Purchase #3 $212.65   13.781%   $241.9553   $241.96   $241.95   $242.00  
  Purchase #4 $51.85   13.243%   $58.7165   $58.72   $58.70   $58.70  
  Purchase #5 $38.74   9.562%   $42.4443   $42.44   $42.45   $42.40  
  Purchase #6 $112.46   5.562%   $118.715   $118.72   $118.70   $118.70  
  Purchase #7 $232.44   11.552%   $259.2915   $259.29   $259.30   $259.30  
  7 purchase totals = $778.00       $867.9537   $867.96   $867.90   $868.00