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 $93.47   3.361%   $96.6115   $96.61   $96.60   $96.60  
  Purchase #2 $22.53   3.856%   $23.3988   $23.40   $23.40   $23.40  
  Purchase #3 $67.79   7.369%   $72.7854   $72.79   $72.80   $72.80  
  Purchase #4 $63.25   5.798%   $66.9172   $66.92   $66.90   $66.90  
  Purchase #5 $130.67   9.750%   $143.4103   $143.41   $143.40   $143.40  
  Purchase #6 $97.36   10.418%   $107.503   $107.50   $107.50   $107.50  
  Purchase #7 $10.58   7.870%   $11.4126   $11.41   $11.40   $11.40  
  7 purchase totals = $485.65       $522.0388   $522.04   $522.00   $522.00