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 $61.25   7.602%   $65.9062   $65.91   $65.90   $65.90  
  Purchase #2 $124.50   11.447%   $138.7515   $138.75   $138.75   $138.80  
  Purchase #3 $81.25   13.841%   $92.4958   $92.50   $92.50   $92.50  
  Purchase #4 $213.90   11.311%   $238.0942   $238.09   $238.10   $238.10  
  Purchase #5 $68.67   9.208%   $74.9931   $74.99   $75.00   $75.00  
  Purchase #6 $178.79   7.835%   $192.7982   $192.80   $192.80   $192.80  
  Purchase #7 $67.88   8.466%   $73.6267   $73.63   $73.65   $73.60  
  7 purchase totals = $796.24       $876.6657   $876.67   $876.70   $876.70