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 $119.89   12.433%   $134.7959   $134.80   $134.80   $134.80  
  Purchase #2 $53.75   7.231%   $57.6367   $57.64   $57.65   $57.60  
  Purchase #3 $197.45   12.372%   $221.8785   $221.88   $221.90   $221.90  
  Purchase #4 $23.27   12.567%   $26.1943   $26.19   $26.20   $26.20  
  Purchase #5 $51.84   9.201%   $56.6098   $56.61   $56.60   $56.60  
  Purchase #6 $151.74   13.118%   $171.6453   $171.65   $171.65   $171.60  
  Purchase #7 $186.38   3.600%   $193.0897   $193.09   $193.10   $193.10  
  7 purchase totals = $784.32       $861.8502   $861.86   $861.90   $861.80