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 $178.33   9.139%   $194.6276   $194.63   $194.65   $194.60  
  Purchase #2 $238.55   9.805%   $261.9398   $261.94   $261.95   $261.90  
  Purchase #3 $61.26   13.159%   $69.3212   $69.32   $69.30   $69.30  
  Purchase #4 $241.32   10.592%   $266.8806   $266.88   $266.90   $266.90  
  Purchase #5 $168.92   10.642%   $186.8965   $186.90   $186.90   $186.90  
  Purchase #6 $96.28   4.458%   $100.5722   $100.57   $100.55   $100.60  
  Purchase #7 $249.79   6.686%   $266.491   $266.49   $266.50   $266.50  
  7 purchase totals = $1,234.45       $1,346.7289   $1,346.73   $1,346.75   $1,346.70