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 $68.68   11.376%   $76.493   $76.49   $76.50   $76.50  
  Purchase #2 $237.55   10.228%   $261.8466   $261.85   $261.85   $261.80  
  Purchase #3 $175.84   3.503%   $181.9997   $182.00   $182.00   $182.00  
  Purchase #4 $77.53   11.258%   $86.2583   $86.26   $86.25   $86.30  
  Purchase #5 $127.68   10.427%   $140.9932   $140.99   $141.00   $141.00  
  Purchase #6 $21.59   4.869%   $22.6412   $22.64   $22.65   $22.60  
  Purchase #7 $33.71   5.317%   $35.5024   $35.50   $35.50   $35.50  
  7 purchase totals = $742.58       $805.7344   $805.73   $805.75   $805.70