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 $156.31   11.572%   $174.3982   $174.40   $174.40   $174.40  
  Purchase #2 $108.46   10.590%   $119.9459   $119.95   $119.95   $119.90  
  Purchase #3 $234.82   10.708%   $259.9645   $259.96   $259.95   $260.00  
  Purchase #4 $162.98   13.540%   $185.0475   $185.05   $185.05   $185.00  
  Purchase #5 $122.89   10.231%   $135.4629   $135.46   $135.45   $135.50  
  Purchase #6 $67.46   8.604%   $73.2643   $73.26   $73.25   $73.30  
  Purchase #7 $78.33   5.571%   $82.6938   $82.69   $82.70   $82.70  
  7 purchase totals = $931.25       $1,030.7771   $1,030.77   $1,030.75   $1,030.80