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 $86.73   7.665%   $93.3779   $93.38   $93.40   $93.40  
  Purchase #2 $147.49   4.602%   $154.2775   $154.28   $154.30   $154.30  
  Purchase #3 $58.82   8.305%   $63.705   $63.71   $63.70   $63.70  
  Purchase #4 $89.83   4.175%   $93.5804   $93.58   $93.60   $93.60  
  Purchase #5 $92.50   12.642%   $104.1939   $104.19   $104.20   $104.20  
  Purchase #6 $72.27   3.513%   $74.8088   $74.81   $74.80   $74.80  
  Purchase #7 $68.92   4.785%   $72.2178   $72.22   $72.20   $72.20  
  7 purchase totals = $616.56       $656.1613   $656.17   $656.20   $656.20