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 $53.65   11.354%   $59.7414   $59.74   $59.75   $59.70  
  Purchase #2 $228.45   12.678%   $257.4129   $257.41   $257.40   $257.40  
  Purchase #3 $100.77   12.589%   $113.4559   $113.46   $113.45   $113.50  
  Purchase #4 $217.60   12.641%   $245.1068   $245.11   $245.10   $245.10  
  Purchase #5 $193.72   8.755%   $210.6802   $210.68   $210.70   $210.70  
  Purchase #6 $58.58   3.215%   $60.4633   $60.46   $60.45   $60.50  
  Purchase #7 $83.75   3.424%   $86.6176   $86.62   $86.60   $86.60  
  7 purchase totals = $936.52       $1,033.4781   $1,033.48   $1,033.45   $1,033.50