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 $91.99   13.344%   $104.2651   $104.27   $104.25   $104.30  
  Purchase #2 $73.73   5.162%   $77.5359   $77.54   $77.55   $77.50  
  Purchase #3 $150.56   6.711%   $160.6641   $160.66   $160.65   $160.70  
  Purchase #4 $231.67   7.299%   $248.5796   $248.58   $248.60   $248.60  
  Purchase #5 $44.88   12.734%   $50.595   $50.60   $50.60   $50.60  
  Purchase #6 $245.39   5.396%   $258.6312   $258.63   $258.65   $258.60  
  Purchase #7 $57.94   10.502%   $64.0249   $64.02   $64.00   $64.00  
  7 purchase totals = $896.16       $964.2958   $964.30   $964.30   $964.30