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 $244.87   8.491%   $265.6619   $265.66   $265.65   $265.70  
  Purchase #2 $211.74   13.292%   $239.8845   $239.88   $239.90   $239.90  
  Purchase #3 $70.26   12.660%   $79.1549   $79.15   $79.15   $79.20  
  Purchase #4 $200.64   10.291%   $221.2879   $221.29   $221.30   $221.30  
  Purchase #5 $63.93   11.127%   $71.0435   $71.04   $71.05   $71.00  
  Purchase #6 $238.63   8.518%   $258.9565   $258.96   $258.95   $259.00  
  Purchase #7 $185.63   11.283%   $206.5746   $206.57   $206.55   $206.60  
  7 purchase totals = $1,215.70       $1,342.5638   $1,342.55   $1,342.55   $1,342.70