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 $81.78   12.566%   $92.0565   $92.06   $92.05   $92.10  
  Purchase #2 $45.49   13.611%   $51.6816   $51.68   $51.70   $51.70  
  Purchase #3 $103.48   13.525%   $117.4757   $117.48   $117.50   $117.50  
  Purchase #4 $208.53   12.612%   $234.8298   $234.83   $234.85   $234.80  
  Purchase #5 $51.43   10.685%   $56.9253   $56.93   $56.95   $56.90  
  Purchase #6 $94.38   8.499%   $102.4014   $102.40   $102.40   $102.40  
  Purchase #7 $41.44   9.747%   $45.4792   $45.48   $45.50   $45.50  
  7 purchase totals = $626.53       $700.8495   $700.86   $700.95   $700.90