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 $24.48   5.595%   $25.8497   $25.85   $25.85   $25.80  
  Purchase #2 $72.39   6.196%   $76.8753   $76.88   $76.90   $76.90  
  Purchase #3 $177.30   7.865%   $191.2446   $191.24   $191.25   $191.20  
  Purchase #4 $246.76   7.209%   $264.5489   $264.55   $264.55   $264.50  
  Purchase #5 $186.36   13.676%   $211.8466   $211.85   $211.85   $211.80  
  Purchase #6 $238.78   9.306%   $261.0009   $261.00   $261.00   $261.00  
  Purchase #7 $109.70   11.458%   $122.2694   $122.27   $122.25   $122.30  
  7 purchase totals = $1,055.77       $1,153.6354   $1,153.64   $1,153.65   $1,153.50