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 $98.58   4.378%   $102.8958   $102.90   $102.90   $102.90  
  Purchase #2 $211.88   13.600%   $240.6957   $240.70   $240.70   $240.70  
  Purchase #3 $167.33   5.265%   $176.1399   $176.14   $176.15   $176.10  
  Purchase #4 $78.95   6.593%   $84.1552   $84.16   $84.15   $84.20  
  Purchase #5 $52.75   13.833%   $60.0469   $60.05   $60.05   $60.00  
  Purchase #6 $146.54   11.182%   $162.9261   $162.93   $162.95   $162.90  
  Purchase #7 $56.55   8.159%   $61.1639   $61.16   $61.15   $61.20  
  7 purchase totals = $812.58       $888.0235   $888.04   $888.05   $888.00