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 $50.76   6.763%   $54.1929   $54.19   $54.20   $54.20  
  Purchase #2 $168.65   7.845%   $181.8806   $181.88   $181.90   $181.90  
  Purchase #3 $173.68   11.140%   $193.028   $193.03   $193.05   $193.00  
  Purchase #4 $157.80   8.529%   $171.2588   $171.26   $171.25   $171.30  
  Purchase #5 $132.55   5.616%   $139.994   $139.99   $140.00   $140.00  
  Purchase #6 $192.79   13.381%   $218.5872   $218.59   $218.60   $218.60  
  Purchase #7 $105.95   12.538%   $119.234   $119.23   $119.25   $119.20  
  7 purchase totals = $982.18       $1,078.1755   $1,078.17   $1,078.25   $1,078.20