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 $96.61   12.862%   $109.036   $109.04   $109.05   $109.00  
  Purchase #2 $87.55   12.790%   $98.7476   $98.75   $98.75   $98.70  
  Purchase #3 $49.77   13.522%   $56.4999   $56.50   $56.50   $56.50  
  Purchase #4 $247.62   7.452%   $266.0726   $266.07   $266.05   $266.10  
  Purchase #5 $28.42   11.486%   $31.6843   $31.68   $31.70   $31.70  
  Purchase #6 $167.88   6.102%   $178.124   $178.12   $178.10   $178.10  
  Purchase #7 $138.73   7.352%   $148.9294   $148.93   $148.95   $148.90  
  7 purchase totals = $816.58       $889.0938   $889.09   $889.10   $889.00