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 $23.98   6.652%   $25.5751   $25.58   $25.60   $25.60  
  Purchase #2 $93.89   8.322%   $101.7035   $101.70   $101.70   $101.70  
  Purchase #3 $10.69   9.798%   $11.7374   $11.74   $11.75   $11.70  
  Purchase #4 $86.88   6.537%   $92.5593   $92.56   $92.55   $92.60  
  Purchase #5 $115.70   8.621%   $125.6745   $125.67   $125.65   $125.70  
  Purchase #6 $180.80   13.688%   $205.5479   $205.55   $205.55   $205.50  
  Purchase #7 $119.29   10.133%   $131.3777   $131.38   $131.40   $131.40  
  7 purchase totals = $631.23       $694.1754   $694.18   $694.20   $694.20