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 $126.67   5.448%   $133.571   $133.57   $133.55   $133.60  
  Purchase #2 $187.32   11.355%   $208.5902   $208.59   $208.60   $208.60  
  Purchase #3 $24.78   9.207%   $27.0615   $27.06   $27.05   $27.10  
  Purchase #4 $145.36   6.119%   $154.2546   $154.25   $154.25   $154.30  
  Purchase #5 $29.41   11.326%   $32.741   $32.74   $32.75   $32.70  
  Purchase #6 $105.50   12.772%   $118.9745   $118.97   $118.95   $119.00  
  Purchase #7 $236.80   5.163%   $249.026   $249.03   $249.05   $249.00  
  7 purchase totals = $855.84       $924.2188   $924.21   $924.20   $924.30