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 $64.91   4.212%   $67.644   $67.64   $67.65   $67.60  
  Purchase #2 $190.77   7.460%   $205.0014   $205.00   $205.00   $205.00  
  Purchase #3 $238.53   9.827%   $261.9703   $261.97   $261.95   $262.00  
  Purchase #4 $246.44   8.175%   $266.5865   $266.59   $266.60   $266.60  
  Purchase #5 $240.51   7.587%   $258.7575   $258.76   $258.75   $258.80  
  Purchase #6 $232.67   12.627%   $262.0492   $262.05   $262.05   $262.00  
  Purchase #7 $53.38   9.824%   $58.6241   $58.62   $58.60   $58.60  
  7 purchase totals = $1,267.21       $1,380.6330   $1,380.63   $1,380.60   $1,380.60