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 $86.40   13.811%   $98.3327   $98.33   $98.35   $98.30  
  Purchase #2 $58.94   12.672%   $66.4089   $66.41   $66.40   $66.40  
  Purchase #3 $241.25   10.477%   $266.5258   $266.53   $266.55   $266.50  
  Purchase #4 $205.67   4.624%   $215.1802   $215.18   $215.20   $215.20  
  Purchase #5 $161.58   8.502%   $175.3175   $175.32   $175.30   $175.30  
  Purchase #6 $51.51   4.247%   $53.6976   $53.70   $53.70   $53.70  
  Purchase #7 $66.99   5.489%   $70.6671   $70.67   $70.65   $70.70  
  7 purchase totals = $872.34       $946.1298   $946.14   $946.15   $946.10