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 $68.91   11.251%   $76.6631   $76.66   $76.65   $76.70  
  Purchase #2 $122.72   13.715%   $139.551   $139.55   $139.55   $139.60  
  Purchase #3 $29.95   9.814%   $32.8893   $32.89   $32.90   $32.90  
  Purchase #4 $164.33   12.481%   $184.84   $184.84   $184.85   $184.80  
  Purchase #5 $27.58   5.348%   $29.055   $29.06   $29.05   $29.10  
  Purchase #6 $221.48   7.789%   $238.7311   $238.73   $238.75   $238.70  
  Purchase #7 $241.54   4.513%   $252.4407   $252.44   $252.45   $252.40  
  7 purchase totals = $876.51       $954.1702   $954.17   $954.20   $954.20