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 $237.46   13.493%   $269.5005   $269.50   $269.50   $269.50  
  Purchase #2 $85.63   3.413%   $88.5526   $88.55   $88.55   $88.60  
  Purchase #3 $143.44   9.407%   $156.9334   $156.93   $156.95   $156.90  
  Purchase #4 $33.31   8.291%   $36.0717   $36.07   $36.05   $36.10  
  Purchase #5 $13.26   9.267%   $14.4888   $14.49   $14.50   $14.50  
  Purchase #6 $118.43   8.648%   $128.6718   $128.67   $128.65   $128.70  
  Purchase #7 $48.34   3.209%   $49.8912   $49.89   $49.90   $49.90  
  7 purchase totals = $679.87       $744.1100   $744.10   $744.10   $744.20