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 $205.51   3.404%   $212.5056   $212.51   $212.50   $212.50  
  Purchase #2 $198.74   11.873%   $222.3364   $222.34   $222.35   $222.30  
  Purchase #3 $247.91   5.551%   $261.6715   $261.67   $261.65   $261.70  
  Purchase #4 $14.39   8.648%   $15.6344   $15.63   $15.65   $15.60  
  Purchase #5 $204.28   12.560%   $229.9376   $229.94   $229.95   $229.90  
  Purchase #6 $13.99   13.644%   $15.8988   $15.90   $15.90   $15.90  
  Purchase #7 $239.34   3.267%   $247.1592   $247.16   $247.15   $247.20  
  7 purchase totals = $1,124.16       $1,205.1435   $1,205.15   $1,205.15   $1,205.10