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 $247.26   5.225%   $260.1793   $260.18   $260.20   $260.20  
  Purchase #2 $178.37   11.413%   $198.7274   $198.73   $198.75   $198.70  
  Purchase #3 $112.57   10.139%   $123.9835   $123.98   $124.00   $124.00  
  Purchase #4 $121.99   10.762%   $135.1186   $135.12   $135.10   $135.10  
  Purchase #5 $14.74   12.676%   $16.6084   $16.61   $16.60   $16.60  
  Purchase #6 $245.46   8.574%   $266.5057   $266.51   $266.50   $266.50  
  Purchase #7 $146.91   11.590%   $163.9369   $163.94   $163.95   $163.90  
  7 purchase totals = $1,067.30       $1,165.0598   $1,165.07   $1,165.10   $1,165.00