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 $162.43   6.792%   $173.4622   $173.46   $173.45   $173.50  
  Purchase #2 $114.88   13.593%   $130.4956   $130.50   $130.50   $130.50  
  Purchase #3 $126.47   12.807%   $142.667   $142.67   $142.65   $142.70  
  Purchase #4 $230.89   3.869%   $239.8231   $239.82   $239.80   $239.80  
  Purchase #5 $186.75   8.438%   $202.508   $202.51   $202.50   $202.50  
  Purchase #6 $81.80   10.678%   $90.5346   $90.53   $90.55   $90.50  
  Purchase #7 $236.94   12.826%   $267.3299   $267.33   $267.35   $267.30  
  7 purchase totals = $1,140.16       $1,246.8204   $1,246.82   $1,246.80   $1,246.80