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 $56.67   11.823%   $63.3701   $63.37   $63.35   $63.40  
  Purchase #2 $213.63   13.433%   $242.3269   $242.33   $242.35   $242.30  
  Purchase #3 $50.94   3.128%   $52.5334   $52.53   $52.55   $52.50  
  Purchase #4 $206.58   3.299%   $213.3951   $213.40   $213.40   $213.40  
  Purchase #5 $140.57   10.223%   $154.9405   $154.94   $154.95   $154.90  
  Purchase #6 $138.65   6.639%   $147.855   $147.86   $147.85   $147.90  
  Purchase #7 $26.44   5.171%   $27.8072   $27.81   $27.80   $27.80  
  7 purchase totals = $833.48       $902.2282   $902.24   $902.25   $902.20