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 $232.53   11.581%   $259.4593   $259.46   $259.45   $259.50  
  Purchase #2 $208.80   9.172%   $227.9511   $227.95   $227.95   $228.00  
  Purchase #3 $34.88   10.639%   $38.5909   $38.59   $38.60   $38.60  
  Purchase #4 $105.29   12.197%   $118.1322   $118.13   $118.15   $118.10  
  Purchase #5 $205.84   11.850%   $230.232   $230.23   $230.25   $230.20  
  Purchase #6 $143.93   5.454%   $151.7799   $151.78   $151.80   $151.80  
  Purchase #7 $154.66   3.723%   $160.418   $160.42   $160.40   $160.40  
  7 purchase totals = $1,085.93       $1,186.5634   $1,186.56   $1,186.60   $1,186.60