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 $49.73   7.559%   $53.4891   $53.49   $53.50   $53.50  
  Purchase #2 $103.68   7.739%   $111.7038   $111.70   $111.70   $111.70  
  Purchase #3 $224.93   11.858%   $251.6022   $251.60   $251.60   $251.60  
  Purchase #4 $73.44   12.563%   $82.6663   $82.67   $82.65   $82.70  
  Purchase #5 $59.89   11.755%   $66.9301   $66.93   $66.95   $66.90  
  Purchase #6 $101.45   11.864%   $113.486   $113.49   $113.50   $113.50  
  Purchase #7 $219.32   7.709%   $236.2274   $236.23   $236.25   $236.20  
  7 purchase totals = $832.44       $916.1049   $916.11   $916.15   $916.10