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 $238.45   9.461%   $261.0098   $261.01   $261.00   $261.00  
  Purchase #2 $103.60   3.606%   $107.3358   $107.34   $107.35   $107.30  
  Purchase #3 $156.75   6.221%   $166.5014   $166.50   $166.50   $166.50  
  Purchase #4 $134.77   10.849%   $149.3912   $149.39   $149.40   $149.40  
  Purchase #5 $115.81   6.426%   $123.252   $123.25   $123.25   $123.30  
  Purchase #6 $127.30   12.102%   $142.7058   $142.71   $142.70   $142.70  
  Purchase #7 $88.90   5.362%   $93.6668   $93.67   $93.65   $93.70  
  7 purchase totals = $965.58       $1,043.8628   $1,043.87   $1,043.85   $1,043.90