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 $22.76   8.708%   $24.7419   $24.74   $24.75   $24.70  
  Purchase #2 $180.58   13.727%   $205.3682   $205.37   $205.35   $205.40  
  Purchase #3 $242.95   6.280%   $258.2073   $258.21   $258.20   $258.20  
  Purchase #4 $112.36   6.366%   $119.5128   $119.51   $119.50   $119.50  
  Purchase #5 $234.63   12.783%   $264.6228   $264.62   $264.60   $264.60  
  Purchase #6 $128.41   6.555%   $136.8273   $136.83   $136.85   $136.80  
  Purchase #7 $53.88   11.134%   $59.879   $59.88   $59.90   $59.90  
  7 purchase totals = $975.57       $1,069.1593   $1,069.16   $1,069.15   $1,069.10