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 $249.66   9.560%   $273.5275   $273.53   $273.55   $273.50  
  Purchase #2 $230.55   13.357%   $261.3446   $261.34   $261.35   $261.30  
  Purchase #3 $129.44   9.780%   $142.0992   $142.10   $142.10   $142.10  
  Purchase #4 $24.69   9.513%   $27.0388   $27.04   $27.05   $27.00  
  Purchase #5 $49.68   9.493%   $54.3961   $54.40   $54.40   $54.40  
  Purchase #6 $135.75   11.669%   $151.5907   $151.59   $151.60   $151.60  
  Purchase #7 $166.93   9.837%   $183.3509   $183.35   $183.35   $183.40  
  7 purchase totals = $986.70       $1,093.3478   $1,093.35   $1,093.40   $1,093.30