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 $250.95   13.661%   $285.2323   $285.23   $285.25   $285.20  
  Purchase #2 $169.81   13.836%   $193.3049   $193.30   $193.30   $193.30  
  Purchase #3 $158.71   13.778%   $180.5771   $180.58   $180.60   $180.60  
  Purchase #4 $233.58   11.152%   $259.6288   $259.63   $259.65   $259.60  
  Purchase #5 $15.91   9.568%   $17.4323   $17.43   $17.45   $17.40  
  Purchase #6 $87.47   12.156%   $98.1029   $98.10   $98.10   $98.10  
  Purchase #7 $64.83   9.216%   $70.8047   $70.80   $70.80   $70.80  
  7 purchase totals = $981.26       $1,105.0830   $1,105.07   $1,105.15   $1,105.00