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 $246.95   4.723%   $258.6134   $258.61   $258.60   $258.60  
  Purchase #2 $58.66   11.220%   $65.2417   $65.24   $65.25   $65.20  
  Purchase #3 $207.79   3.205%   $214.4497   $214.45   $214.45   $214.40  
  Purchase #4 $248.41   3.160%   $256.2598   $256.26   $256.25   $256.30  
  Purchase #5 $169.26   10.344%   $186.7683   $186.77   $186.75   $186.80  
  Purchase #6 $20.59   13.597%   $23.3896   $23.39   $23.40   $23.40  
  Purchase #7 $201.42   13.108%   $227.8221   $227.82   $227.80   $227.80  
  7 purchase totals = $1,153.08       $1,232.5446   $1,232.54   $1,232.50   $1,232.50