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 $183.36   11.174%   $203.8486   $203.85   $203.85   $203.80  
  Purchase #2 $185.95   12.361%   $208.9353   $208.94   $208.95   $208.90  
  Purchase #3 $44.53   9.116%   $48.5894   $48.59   $48.60   $48.60  
  Purchase #4 $193.30   4.777%   $202.5339   $202.53   $202.55   $202.50  
  Purchase #5 $55.69   8.273%   $60.2972   $60.30   $60.30   $60.30  
  Purchase #6 $236.37   12.785%   $266.5899   $266.59   $266.60   $266.60  
  Purchase #7 $214.50   5.801%   $226.9431   $226.94   $226.95   $226.90  
  7 purchase totals = $1,113.70       $1,217.7374   $1,217.74   $1,217.80   $1,217.60