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 $51.57   13.599%   $58.583   $58.58   $58.60   $58.60  
  Purchase #2 $246.58   8.395%   $267.2804   $267.28   $267.30   $267.30  
  Purchase #3 $63.92   10.628%   $70.7134   $70.71   $70.70   $70.70  
  Purchase #4 $158.73   9.265%   $173.4363   $173.44   $173.45   $173.40  
  Purchase #5 $226.40   11.587%   $252.633   $252.63   $252.65   $252.60  
  Purchase #6 $84.85   6.116%   $90.0394   $90.04   $90.05   $90.00  
  Purchase #7 $28.46   13.863%   $32.4054   $32.41   $32.40   $32.40  
  7 purchase totals = $860.51       $945.0909   $945.09   $945.15   $945.00