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 $41.87   3.163%   $43.1943   $43.19   $43.20   $43.20  
  Purchase #2 $33.54   4.276%   $34.9742   $34.97   $34.95   $35.00  
  Purchase #3 $26.72   10.394%   $29.4973   $29.50   $29.50   $29.50  
  Purchase #4 $237.63   13.447%   $269.5841   $269.58   $269.60   $269.60  
  Purchase #5 $116.72   5.544%   $123.191   $123.19   $123.20   $123.20  
  Purchase #6 $204.36   10.119%   $225.0392   $225.04   $225.05   $225.00  
  Purchase #7 $168.40   3.779%   $174.7638   $174.76   $174.75   $174.80  
  7 purchase totals = $829.24       $900.2439   $900.23   $900.25   $900.30