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 $250.87   3.579%   $259.8486   $259.85   $259.85   $259.80  
  Purchase #2 $225.57   7.193%   $241.7953   $241.80   $241.80   $241.80  
  Purchase #3 $211.79   8.276%   $229.3177   $229.32   $229.30   $229.30  
  Purchase #4 $57.93   11.556%   $64.6244   $64.62   $64.60   $64.60  
  Purchase #5 $227.46   8.515%   $246.8282   $246.83   $246.85   $246.80  
  Purchase #6 $239.90   8.225%   $259.6318   $259.63   $259.65   $259.60  
  Purchase #7 $60.57   4.498%   $63.2944   $63.29   $63.30   $63.30  
  7 purchase totals = $1,274.09       $1,365.3404   $1,365.34   $1,365.35   $1,365.20