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 $249.59   5.191%   $262.5462   $262.55   $262.55   $262.50  
  Purchase #2 $202.59   8.204%   $219.2105   $219.21   $219.20   $219.20  
  Purchase #3 $29.46   13.683%   $33.491   $33.49   $33.50   $33.50  
  Purchase #4 $115.52   6.477%   $123.0022   $123.00   $123.00   $123.00  
  Purchase #5 $200.54   8.639%   $217.8647   $217.86   $217.85   $217.90  
  Purchase #6 $53.38   8.703%   $58.0257   $58.03   $58.05   $58.00  
  Purchase #7 $236.54   8.665%   $257.0362   $257.04   $257.05   $257.00  
  7 purchase totals = $1,087.62       $1,171.1765   $1,171.18   $1,171.20   $1,171.10