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 $47.83   8.372%   $51.8343   $51.83   $51.85   $51.80  
  Purchase #2 $89.97   5.619%   $95.0254   $95.03   $95.05   $95.00  
  Purchase #3 $85.64   8.324%   $92.7687   $92.77   $92.75   $92.80  
  Purchase #4 $128.86   8.639%   $139.9922   $139.99   $140.00   $140.00  
  Purchase #5 $43.94   4.575%   $45.9503   $45.95   $45.95   $46.00  
  Purchase #6 $246.73   9.258%   $269.5723   $269.57   $269.55   $269.60  
  Purchase #7 $231.59   8.853%   $252.0927   $252.09   $252.10   $252.10  
  7 purchase totals = $874.56       $947.2359   $947.23   $947.25   $947.30