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 $118.93   3.462%   $123.0474   $123.05   $123.05   $123.00  
  Purchase #2 $153.77   3.813%   $159.6333   $159.63   $159.65   $159.60  
  Purchase #3 $123.45   5.490%   $130.2274   $130.23   $130.25   $130.20  
  Purchase #4 $61.36   4.156%   $63.9101   $63.91   $63.90   $63.90  
  Purchase #5 $236.69   13.207%   $267.9496   $267.95   $267.95   $267.90  
  Purchase #6 $13.56   10.703%   $15.0113   $15.01   $15.00   $15.00  
  Purchase #7 $10.73   6.420%   $11.4189   $11.42   $11.40   $11.40  
  7 purchase totals = $718.49       $771.1980   $771.20   $771.20   $771.00