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 $113.83   11.801%   $127.2631   $127.26   $127.25   $127.30  
  Purchase #2 $239.81   8.206%   $259.4888   $259.49   $259.50   $259.50  
  Purchase #3 $133.54   8.369%   $144.716   $144.72   $144.70   $144.70  
  Purchase #4 $182.49   3.204%   $188.337   $188.34   $188.35   $188.30  
  Purchase #5 $186.98   13.184%   $211.6314   $211.63   $211.65   $211.60  
  Purchase #6 $199.79   4.592%   $208.9644   $208.96   $208.95   $209.00  
  Purchase #7 $21.31   5.210%   $22.4203   $22.42   $22.40   $22.40  
  7 purchase totals = $1,077.75       $1,162.8210   $1,162.82   $1,162.80   $1,162.80