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 $49.31   11.527%   $54.994   $54.99   $55.00   $55.00  
  Purchase #2 $168.34   13.822%   $191.608   $191.61   $191.60   $191.60  
  Purchase #3 $126.90   11.631%   $141.6597   $141.66   $141.65   $141.70  
  Purchase #4 $199.84   7.824%   $215.4755   $215.48   $215.50   $215.50  
  Purchase #5 $59.33   6.611%   $63.2523   $63.25   $63.25   $63.30  
  Purchase #6 $114.88   12.795%   $129.5789   $129.58   $129.60   $129.60  
  Purchase #7 $128.45   9.145%   $140.1968   $140.20   $140.20   $140.20  
  7 purchase totals = $847.05       $936.7652   $936.77   $936.80   $936.90