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 $46.94   11.846%   $52.5005   $52.50   $52.50   $52.50  
  Purchase #2 $214.91   4.498%   $224.5767   $224.58   $224.60   $224.60  
  Purchase #3 $167.49   4.193%   $174.5129   $174.51   $174.50   $174.50  
  Purchase #4 $190.40   8.524%   $206.6297   $206.63   $206.65   $206.60  
  Purchase #5 $101.35   10.676%   $112.1701   $112.17   $112.15   $112.20  
  Purchase #6 $60.58   10.379%   $66.8676   $66.87   $66.85   $66.90  
  Purchase #7 $248.93   4.838%   $260.9732   $260.97   $260.95   $261.00  
  7 purchase totals = $1,030.60       $1,098.2307   $1,098.23   $1,098.20   $1,098.30