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 $197.88   12.556%   $222.7258   $222.73   $222.75   $222.70  
  Purchase #2 $95.97   8.658%   $104.2791   $104.28   $104.30   $104.30  
  Purchase #3 $88.69   7.861%   $95.6619   $95.66   $95.65   $95.70  
  Purchase #4 $211.63   11.124%   $235.1717   $235.17   $235.15   $235.20  
  Purchase #5 $56.74   13.106%   $64.1763   $64.18   $64.20   $64.20  
  Purchase #6 $57.38   13.728%   $65.2571   $65.26   $65.25   $65.30  
  Purchase #7 $83.89   13.796%   $95.4635   $95.46   $95.45   $95.50  
  7 purchase totals = $792.18       $882.7354   $882.74   $882.75   $882.90