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 $34.87   10.742%   $38.6157   $38.62   $38.60   $38.60  
  Purchase #2 $182.88   12.231%   $205.2481   $205.25   $205.25   $205.20  
  Purchase #3 $39.68   13.711%   $45.1205   $45.12   $45.10   $45.10  
  Purchase #4 $164.57   5.833%   $174.1694   $174.17   $174.15   $174.20  
  Purchase #5 $15.35   10.136%   $16.9059   $16.91   $16.90   $16.90  
  Purchase #6 $157.32   8.718%   $171.0352   $171.04   $171.05   $171.00  
  Purchase #7 $240.65   9.139%   $262.643   $262.64   $262.65   $262.60  
  7 purchase totals = $835.32       $913.7378   $913.75   $913.70   $913.60