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 $233.51   13.468%   $264.9591   $264.96   $264.95   $265.00  
  Purchase #2 $186.65   5.225%   $196.4025   $196.40   $196.40   $196.40  
  Purchase #3 $104.47   11.865%   $116.8654   $116.87   $116.85   $116.90  
  Purchase #4 $219.93   12.259%   $246.8912   $246.89   $246.90   $246.90  
  Purchase #5 $182.45   8.638%   $198.21   $198.21   $198.20   $198.20  
  Purchase #6 $232.63   11.498%   $259.3778   $259.38   $259.40   $259.40  
  Purchase #7 $53.41   10.432%   $58.9817   $58.98   $59.00   $59.00  
  7 purchase totals = $1,213.05       $1,341.6877   $1,341.69   $1,341.70   $1,341.80