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 $22.54   9.714%   $24.7295   $24.73   $24.75   $24.70  
  Purchase #2 $84.43   12.520%   $95.0006   $95.00   $95.00   $95.00  
  Purchase #3 $193.68   9.408%   $211.9014   $211.90   $211.90   $211.90  
  Purchase #4 $100.44   5.716%   $106.1812   $106.18   $106.20   $106.20  
  Purchase #5 $170.44   9.308%   $186.3046   $186.30   $186.30   $186.30  
  Purchase #6 $240.68   11.849%   $269.1982   $269.20   $269.20   $269.20  
  Purchase #7 $9.88   8.295%   $10.6995   $10.70   $10.70   $10.70  
  7 purchase totals = $822.09       $904.0150   $904.01   $904.05   $904.00