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 $239.81   7.822%   $258.5679   $258.57   $258.55   $258.60  
  Purchase #2 $72.42   3.749%   $75.135   $75.14   $75.15   $75.10  
  Purchase #3 $239.54   11.455%   $266.9793   $266.98   $267.00   $267.00  
  Purchase #4 $140.74   4.184%   $146.6286   $146.63   $146.65   $146.60  
  Purchase #5 $54.49   6.767%   $58.1773   $58.18   $58.20   $58.20  
  Purchase #6 $218.41   3.710%   $226.513   $226.51   $226.50   $226.50  
  Purchase #7 $208.42   13.223%   $235.9794   $235.98   $236.00   $236.00  
  7 purchase totals = $1,173.83       $1,267.9805   $1,267.99   $1,268.05   $1,268.00