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 $152.58   6.141%   $161.9499   $161.95   $161.95   $161.90  
  Purchase #2 $29.82   3.699%   $30.923   $30.92   $30.90   $30.90  
  Purchase #3 $96.26   7.776%   $103.7452   $103.75   $103.75   $103.70  
  Purchase #4 $62.57   4.711%   $65.5177   $65.52   $65.50   $65.50  
  Purchase #5 $224.58   5.134%   $236.1099   $236.11   $236.10   $236.10  
  Purchase #6 $106.38   13.796%   $121.0562   $121.06   $121.05   $121.10  
  Purchase #7 $101.42   12.134%   $113.7263   $113.73   $113.75   $113.70  
  7 purchase totals = $773.61       $833.0282   $833.04   $833.00   $832.90