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 $69.45   10.147%   $76.4971   $76.50   $76.50   $76.50  
  Purchase #2 $208.52   13.441%   $236.5472   $236.55   $236.55   $236.50  
  Purchase #3 $92.89   4.557%   $97.123   $97.12   $97.10   $97.10  
  Purchase #4 $233.71   12.730%   $263.4613   $263.46   $263.45   $263.50  
  Purchase #5 $178.89   8.348%   $193.8237   $193.82   $193.80   $193.80  
  Purchase #6 $53.80   9.640%   $58.9863   $58.99   $59.00   $59.00  
  Purchase #7 $27.86   6.544%   $29.6832   $29.68   $29.70   $29.70  
  7 purchase totals = $865.12       $956.1218   $956.12   $956.10   $956.10