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 $61.37   6.294%   $65.2326   $65.23   $65.25   $65.20  
  Purchase #2 $234.90   5.864%   $248.6745   $248.67   $248.65   $248.70  
  Purchase #3 $122.38   8.849%   $133.2094   $133.21   $133.20   $133.20  
  Purchase #4 $237.52   9.381%   $259.8018   $259.80   $259.80   $259.80  
  Purchase #5 $250.37   11.282%   $278.6167   $278.62   $278.60   $278.60  
  Purchase #6 $137.70   12.406%   $154.7831   $154.78   $154.80   $154.80  
  Purchase #7 $64.61   3.280%   $66.7292   $66.73   $66.75   $66.70  
  7 purchase totals = $1,108.85       $1,207.0473   $1,207.04   $1,207.05   $1,207.00