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 $25.39   7.368%   $27.2607   $27.26   $27.25   $27.30  
  Purchase #2 $130.87   12.685%   $147.4709   $147.47   $147.45   $147.50  
  Purchase #3 $183.28   12.834%   $206.8022   $206.80   $206.80   $206.80  
  Purchase #4 $170.71   6.673%   $182.1015   $182.10   $182.10   $182.10  
  Purchase #5 $241.92   8.477%   $262.4276   $262.43   $262.45   $262.40  
  Purchase #6 $231.90   13.238%   $262.5989   $262.60   $262.60   $262.60  
  Purchase #7 $146.69   10.407%   $161.956   $161.96   $161.95   $162.00  
  7 purchase totals = $1,130.76       $1,250.6178   $1,250.62   $1,250.60   $1,250.70