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 $161.64   13.777%   $183.9091   $183.91   $183.90   $183.90  
  Purchase #2 $109.55   9.304%   $119.7425   $119.74   $119.75   $119.70  
  Purchase #3 $141.64   11.734%   $158.26   $158.26   $158.25   $158.30  
  Purchase #4 $88.55   5.865%   $93.7435   $93.74   $93.75   $93.70  
  Purchase #5 $65.81   3.558%   $68.1515   $68.15   $68.15   $68.20  
  Purchase #6 $24.99   5.511%   $26.3672   $26.37   $26.35   $26.40  
  Purchase #7 $125.83   12.343%   $141.3612   $141.36   $141.35   $141.40  
  7 purchase totals = $718.01       $791.5350   $791.53   $791.50   $791.60