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 $122.62   5.694%   $129.602   $129.60   $129.60   $129.60  
  Purchase #2 $86.94   7.279%   $93.2684   $93.27   $93.25   $93.30  
  Purchase #3 $39.93   3.158%   $41.191   $41.19   $41.20   $41.20  
  Purchase #4 $171.78   11.148%   $190.93   $190.93   $190.95   $190.90  
  Purchase #5 $187.81   7.401%   $201.7098   $201.71   $201.70   $201.70  
  Purchase #6 $102.67   11.340%   $114.3128   $114.31   $114.30   $114.30  
  Purchase #7 $242.43   8.257%   $262.4474   $262.45   $262.45   $262.40  
  7 purchase totals = $954.18       $1,033.4614   $1,033.46   $1,033.45   $1,033.40