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 $62.88   3.378%   $65.0041   $65.00   $65.00   $65.00  
  Purchase #2 $213.80   4.842%   $224.1522   $224.15   $224.15   $224.20  
  Purchase #3 $214.57   13.813%   $244.2086   $244.21   $244.20   $244.20  
  Purchase #4 $14.50   4.629%   $15.1712   $15.17   $15.15   $15.20  
  Purchase #5 $30.44   13.480%   $34.5433   $34.54   $34.55   $34.50  
  Purchase #6 $41.67   4.817%   $43.6772   $43.68   $43.70   $43.70  
  Purchase #7 $248.38   5.860%   $262.9351   $262.94   $262.95   $262.90  
  7 purchase totals = $826.24       $889.6917   $889.69   $889.70   $889.70