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 $23.84   8.369%   $25.8352   $25.84   $25.85   $25.80  
  Purchase #2 $94.82   8.496%   $102.8759   $102.88   $102.90   $102.90  
  Purchase #3 $142.48   8.725%   $154.9114   $154.91   $154.90   $154.90  
  Purchase #4 $208.56   6.108%   $221.2988   $221.30   $221.30   $221.30  
  Purchase #5 $144.38   13.576%   $163.981   $163.98   $164.00   $164.00  
  Purchase #6 $169.57   3.535%   $175.5643   $175.56   $175.55   $175.60  
  Purchase #7 $163.95   9.204%   $179.04   $179.04   $179.05   $179.00  
  7 purchase totals = $947.60       $1,023.5066   $1,023.51   $1,023.55   $1,023.50