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 $186.51   10.495%   $206.0842   $206.08   $206.10   $206.10  
  Purchase #2 $240.37   7.596%   $258.6285   $258.63   $258.65   $258.60  
  Purchase #3 $24.76   7.632%   $26.6497   $26.65   $26.65   $26.60  
  Purchase #4 $206.87   6.404%   $220.118   $220.12   $220.10   $220.10  
  Purchase #5 $198.80   4.855%   $208.4517   $208.45   $208.45   $208.50  
  Purchase #6 $186.70   10.793%   $206.8505   $206.85   $206.85   $206.90  
  Purchase #7 $211.96   6.692%   $226.1444   $226.14   $226.15   $226.10  
  7 purchase totals = $1,255.97       $1,352.9270   $1,352.92   $1,352.95   $1,352.90