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 $226.28   11.483%   $252.2637   $252.26   $252.25   $252.30  
  Purchase #2 $224.29   11.396%   $249.8501   $249.85   $249.85   $249.90  
  Purchase #3 $41.29   12.319%   $46.3765   $46.38   $46.40   $46.40  
  Purchase #4 $53.40   11.624%   $59.6072   $59.61   $59.60   $59.60  
  Purchase #5 $213.41   3.239%   $220.3223   $220.32   $220.30   $220.30  
  Purchase #6 $156.61   11.460%   $174.5575   $174.56   $174.55   $174.60  
  Purchase #7 $8.95   3.768%   $9.2872   $9.29   $9.30   $9.30  
  7 purchase totals = $924.23       $1,012.2645   $1,012.27   $1,012.25   $1,012.40