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 $201.91   11.202%   $224.528   $224.53   $224.55   $224.50  
  Purchase #2 $242.74   6.791%   $259.2245   $259.22   $259.20   $259.20  
  Purchase #3 $33.99   3.327%   $35.1208   $35.12   $35.10   $35.10  
  Purchase #4 $177.38   11.498%   $197.7752   $197.78   $197.80   $197.80  
  Purchase #5 $75.83   4.566%   $79.2924   $79.29   $79.30   $79.30  
  Purchase #6 $247.66   10.562%   $273.8178   $273.82   $273.80   $273.80  
  Purchase #7 $228.63   12.423%   $257.0327   $257.03   $257.05   $257.00  
  7 purchase totals = $1,208.14       $1,326.7914   $1,326.79   $1,326.80   $1,326.70