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 $103.28   5.676%   $109.1422   $109.14   $109.15   $109.10  
  Purchase #2 $28.71   9.662%   $31.484   $31.48   $31.50   $31.50  
  Purchase #3 $27.25   5.799%   $28.8302   $28.83   $28.85   $28.80  
  Purchase #4 $229.61   9.483%   $251.3839   $251.38   $251.40   $251.40  
  Purchase #5 $56.35   13.223%   $63.8012   $63.80   $63.80   $63.80  
  Purchase #6 $76.36   12.716%   $86.0699   $86.07   $86.05   $86.10  
  Purchase #7 $223.89   12.833%   $252.6218   $252.62   $252.60   $252.60  
  7 purchase totals = $745.45       $823.3332   $823.32   $823.35   $823.30