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 $116.81   13.484%   $132.5607   $132.56   $132.55   $132.60  
  Purchase #2 $239.56   4.326%   $249.9234   $249.92   $249.90   $249.90  
  Purchase #3 $235.40   5.215%   $247.6761   $247.68   $247.70   $247.70  
  Purchase #4 $148.68   12.362%   $167.0598   $167.06   $167.05   $167.10  
  Purchase #5 $183.89   3.459%   $190.2508   $190.25   $190.25   $190.30  
  Purchase #6 $137.63   13.837%   $156.6739   $156.67   $156.65   $156.70  
  Purchase #7 $215.96   6.700%   $230.4293   $230.43   $230.45   $230.40  
  7 purchase totals = $1,277.93       $1,374.5740   $1,374.57   $1,374.55   $1,374.70