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 $44.56   6.235%   $47.3383   $47.34   $47.35   $47.30  
  Purchase #2 $181.70   8.245%   $196.6812   $196.68   $196.70   $196.70  
  Purchase #3 $118.61   12.477%   $133.409   $133.41   $133.40   $133.40  
  Purchase #4 $69.79   10.734%   $77.2813   $77.28   $77.30   $77.30  
  Purchase #5 $88.29   11.446%   $98.3957   $98.40   $98.40   $98.40  
  Purchase #6 $90.42   12.326%   $101.5652   $101.57   $101.55   $101.60  
  Purchase #7 $231.61   13.799%   $263.5699   $263.57   $263.55   $263.60  
  7 purchase totals = $824.98       $918.2406   $918.25   $918.25   $918.30