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 $232.35   6.697%   $247.9105   $247.91   $247.90   $247.90  
  Purchase #2 $114.88   3.718%   $119.1512   $119.15   $119.15   $119.20  
  Purchase #3 $197.61   13.627%   $224.5383   $224.54   $224.55   $224.50  
  Purchase #4 $233.95   9.328%   $255.7729   $255.77   $255.75   $255.80  
  Purchase #5 $207.29   12.456%   $233.11   $233.11   $233.10   $233.10  
  Purchase #6 $218.27   9.693%   $239.4269   $239.43   $239.45   $239.40  
  Purchase #7 $43.58   5.427%   $45.9451   $45.95   $45.95   $45.90  
  7 purchase totals = $1,247.93       $1,365.8549   $1,365.86   $1,365.85   $1,365.80