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 $241.52   8.165%   $261.2401   $261.24   $261.25   $261.20  
  Purchase #2 $226.99   10.204%   $250.1521   $250.15   $250.15   $250.20  
  Purchase #3 $30.39   8.422%   $32.9494   $32.95   $32.95   $32.90  
  Purchase #4 $232.86   8.436%   $252.5041   $252.50   $252.50   $252.50  
  Purchase #5 $33.96   12.682%   $38.2668   $38.27   $38.25   $38.30  
  Purchase #6 $229.69   9.404%   $251.29   $251.29   $251.30   $251.30  
  Purchase #7 $211.61   5.113%   $222.4296   $222.43   $222.45   $222.40  
  7 purchase totals = $1,207.02       $1,308.8321   $1,308.83   $1,308.85   $1,308.80