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 $84.91   13.284%   $96.1894   $96.19   $96.20   $96.20  
  Purchase #2 $177.67   7.382%   $190.7856   $190.79   $190.80   $190.80  
  Purchase #3 $83.72   10.416%   $92.4403   $92.44   $92.45   $92.40  
  Purchase #4 $64.25   11.327%   $71.5276   $71.53   $71.55   $71.50  
  Purchase #5 $199.67   3.109%   $205.8777   $205.88   $205.90   $205.90  
  Purchase #6 $134.96   12.398%   $151.6923   $151.69   $151.70   $151.70  
  Purchase #7 $115.46   3.567%   $119.5785   $119.58   $119.60   $119.60  
  7 purchase totals = $860.64       $928.0914   $928.10   $928.20   $928.10