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 $183.75   6.653%   $195.9749   $195.97   $195.95   $196.00  
  Purchase #2 $76.30   4.146%   $79.4634   $79.46   $79.45   $79.50  
  Purchase #3 $162.88   6.136%   $172.8743   $172.87   $172.85   $172.90  
  Purchase #4 $35.31   5.503%   $37.2531   $37.25   $37.25   $37.30  
  Purchase #5 $48.76   3.208%   $50.3242   $50.32   $50.30   $50.30  
  Purchase #6 $212.31   6.859%   $226.8723   $226.87   $226.85   $226.90  
  Purchase #7 $110.76   4.636%   $115.8948   $115.89   $115.90   $115.90  
  7 purchase totals = $830.07       $878.6570   $878.63   $878.55   $878.80