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 $22.66   9.130%   $24.7289   $24.73   $24.75   $24.70  
  Purchase #2 $204.46   4.697%   $214.0635   $214.06   $214.05   $214.10  
  Purchase #3 $68.62   9.457%   $75.1094   $75.11   $75.10   $75.10  
  Purchase #4 $190.64   3.737%   $197.7642   $197.76   $197.75   $197.80  
  Purchase #5 $183.58   8.194%   $198.6225   $198.62   $198.60   $198.60  
  Purchase #6 $26.83   3.158%   $27.6773   $27.68   $27.70   $27.70  
  Purchase #7 $30.50   10.871%   $33.8157   $33.82   $33.80   $33.80  
  7 purchase totals = $727.29       $771.7815   $771.78   $771.75   $771.80