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 $177.31   13.721%   $201.6387   $201.64   $201.65   $201.60  
  Purchase #2 $219.79   3.629%   $227.7662   $227.77   $227.75   $227.80  
  Purchase #3 $245.33   8.747%   $266.789   $266.79   $266.80   $266.80  
  Purchase #4 $198.35   8.844%   $215.8921   $215.89   $215.90   $215.90  
  Purchase #5 $243.71   7.257%   $261.396   $261.40   $261.40   $261.40  
  Purchase #6 $80.25   7.191%   $86.0208   $86.02   $86.00   $86.00  
  Purchase #7 $56.83   5.150%   $59.7567   $59.76   $59.75   $59.80  
  7 purchase totals = $1,221.57       $1,319.2595   $1,319.27   $1,319.25   $1,319.30