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 $108.65   13.573%   $123.3971   $123.40   $123.40   $123.40  
  Purchase #2 $68.79   11.354%   $76.6004   $76.60   $76.60   $76.60  
  Purchase #3 $106.48   11.838%   $119.0851   $119.09   $119.10   $119.10  
  Purchase #4 $88.70   5.145%   $93.2636   $93.26   $93.25   $93.30  
  Purchase #5 $190.34   11.693%   $212.5965   $212.60   $212.60   $212.60  
  Purchase #6 $126.98   7.452%   $136.4425   $136.44   $136.45   $136.40  
  Purchase #7 $65.87   12.358%   $74.0102   $74.01   $74.00   $74.00  
  7 purchase totals = $755.81       $835.3954   $835.40   $835.40   $835.40