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 $219.67   13.238%   $248.7499   $248.75   $248.75   $248.70  
  Purchase #2 $167.39   9.309%   $182.9723   $182.97   $182.95   $183.00  
  Purchase #3 $174.46   5.819%   $184.6118   $184.61   $184.60   $184.60  
  Purchase #4 $169.57   9.700%   $186.0183   $186.02   $186.00   $186.00  
  Purchase #5 $243.43   9.511%   $266.5826   $266.58   $266.60   $266.60  
  Purchase #6 $103.89   8.194%   $112.4027   $112.40   $112.40   $112.40  
  Purchase #7 $44.91   13.432%   $50.9423   $50.94   $50.95   $50.90  
  7 purchase totals = $1,123.32       $1,232.2799   $1,232.27   $1,232.25   $1,232.20