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 $22.38   10.263%   $24.6769   $24.68   $24.70   $24.70  
  Purchase #2 $177.88   8.510%   $193.0176   $193.02   $193.00   $193.00  
  Purchase #3 $53.91   10.714%   $59.6859   $59.69   $59.70   $59.70  
  Purchase #4 $242.74   3.167%   $250.4276   $250.43   $250.45   $250.40  
  Purchase #5 $149.66   12.607%   $168.5276   $168.53   $168.55   $168.50  
  Purchase #6 $5.96   13.578%   $6.7692   $6.77   $6.75   $6.80  
  Purchase #7 $139.53   13.150%   $157.8782   $157.88   $157.90   $157.90  
  7 purchase totals = $792.06       $860.9830   $861.00   $861.05   $861.00