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 $43.34   13.589%   $49.2295   $49.23   $49.25   $49.20  
  Purchase #2 $202.67   11.450%   $225.8757   $225.88   $225.90   $225.90  
  Purchase #3 $161.61   3.678%   $167.554   $167.55   $167.55   $167.60  
  Purchase #4 $10.36   11.347%   $11.5355   $11.54   $11.55   $11.50  
  Purchase #5 $190.31   12.133%   $213.4003   $213.40   $213.40   $213.40  
  Purchase #6 $56.84   3.108%   $58.6066   $58.61   $58.60   $58.60  
  Purchase #7 $61.42   13.483%   $69.7013   $69.70   $69.70   $69.70  
  7 purchase totals = $726.55       $795.9029   $795.91   $795.95   $795.90