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 $196.44   11.312%   $218.6613   $218.66   $218.65   $218.70  
  Purchase #2 $239.30   9.217%   $261.3563   $261.36   $261.35   $261.40  
  Purchase #3 $172.57   9.495%   $188.9555   $188.96   $188.95   $189.00  
  Purchase #4 $121.39   11.873%   $135.8026   $135.80   $135.80   $135.80  
  Purchase #5 $65.44   10.709%   $72.448   $72.45   $72.45   $72.40  
  Purchase #6 $247.84   3.102%   $255.528   $255.53   $255.55   $255.50  
  Purchase #7 $217.33   4.869%   $227.9118   $227.91   $227.90   $227.90  
  7 purchase totals = $1,260.31       $1,360.6635   $1,360.67   $1,360.65   $1,360.70