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 $201.65   6.141%   $214.0333   $214.03   $214.05   $214.00  
  Purchase #2 $139.78   6.506%   $148.8741   $148.87   $148.85   $148.90  
  Purchase #3 $75.26   8.404%   $81.5849   $81.58   $81.60   $81.60  
  Purchase #4 $155.59   7.316%   $166.973   $166.97   $166.95   $167.00  
  Purchase #5 $144.71   5.314%   $152.3999   $152.40   $152.40   $152.40  
  Purchase #6 $5.56   8.358%   $6.0247   $6.02   $6.00   $6.00  
  Purchase #7 $133.61   10.287%   $147.3545   $147.35   $147.35   $147.40  
  7 purchase totals = $856.16       $917.2444   $917.22   $917.20   $917.30