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 $224.79   13.557%   $255.2648   $255.26   $255.25   $255.30  
  Purchase #2 $141.73   10.287%   $156.3098   $156.31   $156.30   $156.30  
  Purchase #3 $200.44   8.408%   $217.293   $217.29   $217.30   $217.30  
  Purchase #4 $22.90   5.624%   $24.1879   $24.19   $24.20   $24.20  
  Purchase #5 $236.50   6.355%   $251.5296   $251.53   $251.55   $251.50  
  Purchase #6 $166.57   12.382%   $187.1947   $187.19   $187.20   $187.20  
  Purchase #7 $54.58   5.773%   $57.7309   $57.73   $57.75   $57.70  
  7 purchase totals = $1,047.51       $1,149.5107   $1,149.50   $1,149.55   $1,149.50