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 $112.32   10.627%   $124.2562   $124.26   $124.25   $124.30  
  Purchase #2 $239.40   6.778%   $255.6265   $255.63   $255.65   $255.60  
  Purchase #3 $33.81   4.297%   $35.2628   $35.26   $35.25   $35.30  
  Purchase #4 $206.93   12.871%   $233.564   $233.56   $233.55   $233.60  
  Purchase #5 $185.45   13.354%   $210.215   $210.22   $210.20   $210.20  
  Purchase #6 $39.52   10.642%   $43.7257   $43.73   $43.75   $43.70  
  Purchase #7 $14.62   13.776%   $16.6341   $16.63   $16.65   $16.60  
  7 purchase totals = $832.05       $919.2843   $919.29   $919.30   $919.30