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 $165.27   6.648%   $176.2571   $176.26   $176.25   $176.30  
  Purchase #2 $236.56   9.765%   $259.6601   $259.66   $259.65   $259.70  
  Purchase #3 $29.99   10.481%   $33.1333   $33.13   $33.15   $33.10  
  Purchase #4 $200.44   5.513%   $211.4903   $211.49   $211.50   $211.50  
  Purchase #5 $21.68   9.222%   $23.6793   $23.68   $23.70   $23.70  
  Purchase #6 $26.32   8.266%   $28.4956   $28.50   $28.50   $28.50  
  Purchase #7 $143.88   5.305%   $151.5128   $151.51   $151.50   $151.50  
  7 purchase totals = $824.14       $884.2285   $884.23   $884.25   $884.30