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 $103.96   9.261%   $113.5877   $113.59   $113.60   $113.60  
  Purchase #2 $173.72   5.298%   $182.9237   $182.92   $182.90   $182.90  
  Purchase #3 $106.94   13.392%   $121.2614   $121.26   $121.25   $121.30  
  Purchase #4 $102.64   3.426%   $106.1564   $106.16   $106.15   $106.20  
  Purchase #5 $154.25   8.388%   $167.1885   $167.19   $167.20   $167.20  
  Purchase #6 $216.99   8.622%   $235.6989   $235.70   $235.70   $235.70  
  Purchase #7 $23.47   10.656%   $25.971   $25.97   $25.95   $26.00  
  7 purchase totals = $881.97       $952.7876   $952.79   $952.75   $952.90