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 $188.49   10.207%   $207.7292   $207.73   $207.75   $207.70  
  Purchase #2 $57.32   10.561%   $63.3736   $63.37   $63.35   $63.40  
  Purchase #3 $89.46   12.712%   $100.8322   $100.83   $100.85   $100.80  
  Purchase #4 $133.91   6.335%   $142.3932   $142.39   $142.40   $142.40  
  Purchase #5 $207.51   10.713%   $229.7405   $229.74   $229.75   $229.70  
  Purchase #6 $218.44   3.634%   $226.3781   $226.38   $226.40   $226.40  
  Purchase #7 $39.74   10.242%   $43.8102   $43.81   $43.80   $43.80  
  7 purchase totals = $934.87       $1,014.2570   $1,014.25   $1,014.30   $1,014.20