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 $47.76   12.337%   $53.6522   $53.65   $53.65   $53.70  
  Purchase #2 $175.36   12.106%   $196.5891   $196.59   $196.60   $196.60  
  Purchase #3 $26.72   3.413%   $27.632   $27.63   $27.65   $27.60  
  Purchase #4 $113.31   12.646%   $127.6392   $127.64   $127.65   $127.60  
  Purchase #5 $67.70   3.247%   $69.8982   $69.90   $69.90   $69.90  
  Purchase #6 $176.85   3.520%   $183.0751   $183.08   $183.10   $183.10  
  Purchase #7 $193.33   4.831%   $202.6698   $202.67   $202.65   $202.70  
  7 purchase totals = $801.03       $861.1556   $861.16   $861.20   $861.20