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 $84.78   11.517%   $94.5441   $94.54   $94.55   $94.50  
  Purchase #2 $228.32   7.711%   $245.9258   $245.93   $245.95   $245.90  
  Purchase #3 $202.56   8.491%   $219.7594   $219.76   $219.75   $219.80  
  Purchase #4 $114.61   12.321%   $128.7311   $128.73   $128.75   $128.70  
  Purchase #5 $202.57   11.517%   $225.9   $225.90   $225.90   $225.90  
  Purchase #6 $21.87   7.185%   $23.4414   $23.44   $23.45   $23.40  
  Purchase #7 $39.25   11.302%   $43.686   $43.69   $43.70   $43.70  
  7 purchase totals = $893.96       $981.9878   $981.99   $982.05   $981.90