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 $201.47   11.856%   $225.3563   $225.36   $225.35   $225.40  
  Purchase #2 $210.42   8.122%   $227.5103   $227.51   $227.50   $227.50  
  Purchase #3 $32.32   7.438%   $34.724   $34.72   $34.70   $34.70  
  Purchase #4 $26.74   12.841%   $30.1737   $30.17   $30.15   $30.20  
  Purchase #5 $204.61   6.225%   $217.347   $217.35   $217.35   $217.30  
  Purchase #6 $14.35   5.593%   $15.1526   $15.15   $15.15   $15.20  
  Purchase #7 $230.96   10.629%   $255.5087   $255.51   $255.50   $255.50  
  7 purchase totals = $920.87       $1,005.7726   $1,005.77   $1,005.70   $1,005.80