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 $240.65   9.601%   $263.7548   $263.75   $263.75   $263.80  
  Purchase #2 $9.82   13.221%   $11.1183   $11.12   $11.10   $11.10  
  Purchase #3 $155.90   7.806%   $168.0696   $168.07   $168.05   $168.10  
  Purchase #4 $49.72   6.108%   $52.7569   $52.76   $52.75   $52.80  
  Purchase #5 $180.43   4.710%   $188.9283   $188.93   $188.95   $188.90  
  Purchase #6 $178.90   12.130%   $200.6006   $200.60   $200.60   $200.60  
  Purchase #7 $34.29   3.724%   $35.567   $35.57   $35.55   $35.60  
  7 purchase totals = $849.71       $920.7955   $920.80   $920.75   $920.90