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 $81.96   5.610%   $86.558   $86.56   $86.55   $86.60  
  Purchase #2 $200.37   7.683%   $215.7644   $215.76   $215.75   $215.80  
  Purchase #3 $38.79   8.704%   $42.1663   $42.17   $42.15   $42.20  
  Purchase #4 $188.96   9.740%   $207.3647   $207.36   $207.35   $207.40  
  Purchase #5 $95.69   7.357%   $102.7299   $102.73   $102.75   $102.70  
  Purchase #6 $248.41   9.410%   $271.7854   $271.79   $271.80   $271.80  
  Purchase #7 $210.93   5.837%   $223.242   $223.24   $223.25   $223.20  
  7 purchase totals = $1,065.11       $1,149.6107   $1,149.61   $1,149.60   $1,149.70