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 $119.81   3.627%   $124.1555   $124.16   $124.15   $124.20  
  Purchase #2 $16.74   5.291%   $17.6257   $17.63   $17.65   $17.60  
  Purchase #3 $69.97   5.334%   $73.7022   $73.70   $73.70   $73.70  
  Purchase #4 $44.29   3.724%   $45.9394   $45.94   $45.95   $45.90  
  Purchase #5 $167.55   13.712%   $190.5245   $190.52   $190.50   $190.50  
  Purchase #6 $188.28   4.271%   $196.3214   $196.32   $196.30   $196.30  
  Purchase #7 $106.94   11.795%   $119.5536   $119.55   $119.55   $119.60  
  7 purchase totals = $713.58       $767.8223   $767.82   $767.80   $767.80