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 $60.34   10.344%   $66.5816   $66.58   $66.60   $66.60  
  Purchase #2 $200.38   8.794%   $218.0014   $218.00   $218.00   $218.00  
  Purchase #3 $44.57   8.114%   $48.1864   $48.19   $48.20   $48.20  
  Purchase #4 $22.55   12.767%   $25.429   $25.43   $25.45   $25.40  
  Purchase #5 $227.83   5.158%   $239.5815   $239.58   $239.60   $239.60  
  Purchase #6 $188.83   9.704%   $207.1541   $207.15   $207.15   $207.20  
  Purchase #7 $135.39   4.185%   $141.0561   $141.06   $141.05   $141.10  
  7 purchase totals = $879.89       $945.9901   $945.99   $946.05   $946.10