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 $9.47   7.309%   $10.1622   $10.16   $10.15   $10.20  
  Purchase #2 $64.73   6.134%   $68.7005   $68.70   $68.70   $68.70  
  Purchase #3 $189.94   11.749%   $212.2561   $212.26   $212.25   $212.30  
  Purchase #4 $58.35   7.752%   $62.8733   $62.87   $62.85   $62.90  
  Purchase #5 $227.68   5.820%   $240.931   $240.93   $240.95   $240.90  
  Purchase #6 $119.99   10.742%   $132.8793   $132.88   $132.90   $132.90  
  Purchase #7 $127.77   6.644%   $136.259   $136.26   $136.25   $136.30  
  7 purchase totals = $797.93       $864.0614   $864.06   $864.05   $864.20