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 $41.48   8.209%   $44.8851   $44.89   $44.90   $44.90  
  Purchase #2 $149.63   4.692%   $156.6506   $156.65   $156.65   $156.70  
  Purchase #3 $192.25   7.827%   $207.2974   $207.30   $207.30   $207.30  
  Purchase #4 $150.57   4.648%   $157.5685   $157.57   $157.55   $157.60  
  Purchase #5 $161.73   4.236%   $168.5809   $168.58   $168.60   $168.60  
  Purchase #6 $55.66   3.537%   $57.6287   $57.63   $57.65   $57.60  
  Purchase #7 $55.83   11.611%   $62.3124   $62.31   $62.30   $62.30  
  7 purchase totals = $807.15       $854.9236   $854.93   $854.95   $855.00