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 $85.56   8.198%   $92.5742   $92.57   $92.55   $92.60  
  Purchase #2 $240.99   8.576%   $261.6573   $261.66   $261.65   $261.70  
  Purchase #3 $155.96   4.713%   $163.3104   $163.31   $163.30   $163.30  
  Purchase #4 $235.93   5.557%   $249.0406   $249.04   $249.05   $249.00  
  Purchase #5 $57.82   13.230%   $65.4696   $65.47   $65.45   $65.50  
  Purchase #6 $147.92   3.558%   $153.183   $153.18   $153.20   $153.20  
  Purchase #7 $183.58   3.622%   $190.2293   $190.23   $190.25   $190.20  
  7 purchase totals = $1,107.76       $1,175.4644   $1,175.46   $1,175.45   $1,175.50