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 $224.25   11.733%   $250.5613   $250.56   $250.55   $250.60  
  Purchase #2 $233.45   8.204%   $252.6022   $252.60   $252.60   $252.60  
  Purchase #3 $103.47   13.465%   $117.4022   $117.40   $117.40   $117.40  
  Purchase #4 $118.56   12.426%   $133.2923   $133.29   $133.30   $133.30  
  Purchase #5 $215.94   13.196%   $244.4354   $244.44   $244.45   $244.40  
  Purchase #6 $169.35   3.162%   $174.7048   $174.70   $174.70   $174.70  
  Purchase #7 $176.69   3.569%   $182.9961   $183.00   $183.00   $183.00  
  7 purchase totals = $1,241.71       $1,355.9943   $1,355.99   $1,356.00   $1,356.00