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 $84.58   12.814%   $95.4181   $95.42   $95.40   $95.40  
  Purchase #2 $36.64   11.192%   $40.7407   $40.74   $40.75   $40.70  
  Purchase #3 $16.46   12.648%   $18.5419   $18.54   $18.55   $18.50  
  Purchase #4 $49.28   7.160%   $52.8084   $52.81   $52.80   $52.80  
  Purchase #5 $27.87   6.275%   $29.6188   $29.62   $29.60   $29.60  
  Purchase #6 $193.36   3.233%   $199.6113   $199.61   $199.60   $199.60  
  Purchase #7 $50.26   8.262%   $54.4125   $54.41   $54.40   $54.40  
  7 purchase totals = $458.45       $491.1517   $491.15   $491.10   $491.00