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 $201.29   11.353%   $224.1425   $224.14   $224.15   $224.10  
  Purchase #2 $155.81   8.240%   $168.6487   $168.65   $168.65   $168.60  
  Purchase #3 $18.73   5.131%   $19.691   $19.69   $19.70   $19.70  
  Purchase #4 $33.72   7.752%   $36.334   $36.33   $36.35   $36.30  
  Purchase #5 $241.82   5.793%   $255.8286   $255.83   $255.85   $255.80  
  Purchase #6 $75.88   6.846%   $81.0747   $81.07   $81.05   $81.10  
  Purchase #7 $227.28   10.327%   $250.7512   $250.75   $250.75   $250.80  
  7 purchase totals = $954.53       $1,036.4707   $1,036.46   $1,036.50   $1,036.40