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 $34.36   6.582%   $36.6216   $36.62   $36.60   $36.60  
  Purchase #2 $58.64   13.581%   $66.6039   $66.60   $66.60   $66.60  
  Purchase #3 $238.73   4.131%   $248.5919   $248.59   $248.60   $248.60  
  Purchase #4 $180.50   13.686%   $205.2032   $205.20   $205.20   $205.20  
  Purchase #5 $247.82   3.839%   $257.3338   $257.33   $257.35   $257.30  
  Purchase #6 $247.70   6.134%   $262.8939   $262.89   $262.90   $262.90  
  Purchase #7 $40.46   5.857%   $42.8297   $42.83   $42.85   $42.80  
  7 purchase totals = $1,048.21       $1,120.0780   $1,120.06   $1,120.10   $1,120.00