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 $51.79   8.265%   $56.0704   $56.07   $56.05   $56.10  
  Purchase #2 $248.94   11.215%   $276.8586   $276.86   $276.85   $276.90  
  Purchase #3 $156.97   4.671%   $164.3021   $164.30   $164.30   $164.30  
  Purchase #4 $206.86   3.449%   $213.9946   $213.99   $214.00   $214.00  
  Purchase #5 $17.82   5.359%   $18.775   $18.78   $18.80   $18.80  
  Purchase #6 $64.70   13.217%   $73.2514   $73.25   $73.25   $73.30  
  Purchase #7 $234.31   12.670%   $263.9971   $264.00   $264.00   $264.00  
  7 purchase totals = $981.39       $1,067.2492   $1,067.25   $1,067.25   $1,067.40