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 $195.61   5.718%   $206.795   $206.80   $206.80   $206.80  
  Purchase #2 $153.94   13.463%   $174.6649   $174.66   $174.65   $174.70  
  Purchase #3 $74.36   12.559%   $83.6989   $83.70   $83.70   $83.70  
  Purchase #4 $67.47   4.859%   $70.7484   $70.75   $70.75   $70.70  
  Purchase #5 $77.52   12.301%   $87.0557   $87.06   $87.05   $87.10  
  Purchase #6 $131.81   6.282%   $140.0903   $140.09   $140.10   $140.10  
  Purchase #7 $220.60   7.342%   $236.7965   $236.80   $236.80   $236.80  
  7 purchase totals = $921.31       $999.8497   $999.86   $999.85   $999.90