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 $175.90   11.799%   $196.6544   $196.65   $196.65   $196.70  
  Purchase #2 $56.60   10.257%   $62.4055   $62.41   $62.40   $62.40  
  Purchase #3 $40.64   12.392%   $45.6761   $45.68   $45.70   $45.70  
  Purchase #4 $79.79   9.339%   $87.2416   $87.24   $87.25   $87.20  
  Purchase #5 $164.73   5.754%   $174.2086   $174.21   $174.20   $174.20  
  Purchase #6 $218.96   9.602%   $239.9845   $239.98   $240.00   $240.00  
  Purchase #7 $23.95   7.575%   $25.7642   $25.76   $25.75   $25.80  
  7 purchase totals = $760.57       $831.9349   $831.93   $831.95   $832.00