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 $24.27   9.484%   $26.5718   $26.57   $26.55   $26.60  
  Purchase #2 $228.73   12.570%   $257.4814   $257.48   $257.50   $257.50  
  Purchase #3 $180.72   7.173%   $193.683   $193.68   $193.70   $193.70  
  Purchase #4 $130.90   10.681%   $144.8814   $144.88   $144.90   $144.90  
  Purchase #5 $42.69   8.206%   $46.1931   $46.19   $46.20   $46.20  
  Purchase #6 $180.57   7.561%   $194.2229   $194.22   $194.20   $194.20  
  Purchase #7 $154.58   9.406%   $169.1198   $169.12   $169.10   $169.10  
  7 purchase totals = $942.46       $1,032.1534   $1,032.14   $1,032.15   $1,032.20