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 $121.46   4.274%   $126.6512   $126.65   $126.65   $126.70  
  Purchase #2 $167.55   11.434%   $186.7077   $186.71   $186.70   $186.70  
  Purchase #3 $57.74   8.592%   $62.701   $62.70   $62.70   $62.70  
  Purchase #4 $211.39   3.102%   $217.9473   $217.95   $217.95   $217.90  
  Purchase #5 $211.87   12.622%   $238.6122   $238.61   $238.60   $238.60  
  Purchase #6 $207.65   10.533%   $229.5218   $229.52   $229.50   $229.50  
  Purchase #7 $156.41   4.159%   $162.9151   $162.92   $162.90   $162.90  
  7 purchase totals = $1,134.07       $1,225.0563   $1,225.06   $1,225.00   $1,225.00