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 $246.51   12.225%   $276.6458   $276.65   $276.65   $276.60  
  Purchase #2 $86.38   12.464%   $97.1464   $97.15   $97.15   $97.10  
  Purchase #3 $62.27   13.288%   $70.5444   $70.54   $70.55   $70.50  
  Purchase #4 $60.26   5.815%   $63.7641   $63.76   $63.75   $63.80  
  Purchase #5 $148.37   10.386%   $163.7797   $163.78   $163.80   $163.80  
  Purchase #6 $52.31   5.653%   $55.2671   $55.27   $55.25   $55.30  
  Purchase #7 $226.71   3.566%   $234.7945   $234.79   $234.80   $234.80  
  7 purchase totals = $882.81       $961.9420   $961.94   $961.95   $961.90