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 $233.41   13.518%   $264.9624   $264.96   $264.95   $265.00  
  Purchase #2 $146.55   10.420%   $161.8205   $161.82   $161.80   $161.80  
  Purchase #3 $242.63   8.398%   $263.0061   $263.01   $263.00   $263.00  
  Purchase #4 $96.77   11.109%   $107.5202   $107.52   $107.50   $107.50  
  Purchase #5 $60.37   10.584%   $66.7596   $66.76   $66.75   $66.80  
  Purchase #6 $82.70   5.584%   $87.318   $87.32   $87.30   $87.30  
  Purchase #7 $119.95   3.524%   $124.177   $124.18   $124.20   $124.20  
  7 purchase totals = $982.38       $1,075.5638   $1,075.57   $1,075.50   $1,075.60