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 $58.32   11.786%   $65.1936   $65.19   $65.20   $65.20  
  Purchase #2 $180.94   5.340%   $190.6022   $190.60   $190.60   $190.60  
  Purchase #3 $126.50   6.152%   $134.2823   $134.28   $134.30   $134.30  
  Purchase #4 $248.49   7.669%   $267.5467   $267.55   $267.55   $267.50  
  Purchase #5 $215.44   3.141%   $222.207   $222.21   $222.20   $222.20  
  Purchase #6 $231.32   10.190%   $254.8915   $254.89   $254.90   $254.90  
  Purchase #7 $23.31   9.136%   $25.4396   $25.44   $25.45   $25.40  
  7 purchase totals = $1,084.32       $1,160.1629   $1,160.16   $1,160.20   $1,160.10