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 $29.87   10.329%   $32.9553   $32.96   $32.95   $33.00  
  Purchase #2 $246.38   7.338%   $264.4594   $264.46   $264.45   $264.50  
  Purchase #3 $31.25   5.281%   $32.9003   $32.90   $32.90   $32.90  
  Purchase #4 $213.62   13.462%   $242.3775   $242.38   $242.40   $242.40  
  Purchase #5 $195.59   9.736%   $214.6326   $214.63   $214.65   $214.60  
  Purchase #6 $186.44   6.617%   $198.7767   $198.78   $198.80   $198.80  
  Purchase #7 $55.89   4.685%   $58.5084   $58.51   $58.50   $58.50  
  7 purchase totals = $959.04       $1,044.6102   $1,044.62   $1,044.65   $1,044.70