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 $104.53   6.855%   $111.6955   $111.70   $111.70   $111.70  
  Purchase #2 $95.54   8.531%   $103.6905   $103.69   $103.70   $103.70  
  Purchase #3 $150.87   8.695%   $163.9881   $163.99   $164.00   $164.00  
  Purchase #4 $149.90   4.214%   $156.2168   $156.22   $156.20   $156.20  
  Purchase #5 $89.85   7.459%   $96.5519   $96.55   $96.55   $96.60  
  Purchase #6 $191.62   8.798%   $208.4787   $208.48   $208.50   $208.50  
  Purchase #7 $113.48   11.226%   $126.2193   $126.22   $126.20   $126.20  
  7 purchase totals = $895.79       $966.8408   $966.85   $966.85   $966.90