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 $61.87   12.518%   $69.6149   $69.61   $69.60   $69.60  
  Purchase #2 $14.84   11.858%   $16.5997   $16.60   $16.60   $16.60  
  Purchase #3 $101.57   13.491%   $115.2728   $115.27   $115.25   $115.30  
  Purchase #4 $124.69   3.519%   $129.0778   $129.08   $129.10   $129.10  
  Purchase #5 $150.40   4.676%   $157.4327   $157.43   $157.45   $157.40  
  Purchase #6 $50.71   8.399%   $54.9691   $54.97   $54.95   $55.00  
  Purchase #7 $22.77   3.611%   $23.5922   $23.59   $23.60   $23.60  
  7 purchase totals = $526.85       $566.5592   $566.55   $566.55   $566.60