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 $108.57   10.291%   $119.7429   $119.74   $119.75   $119.70  
  Purchase #2 $84.64   13.240%   $95.8463   $95.85   $95.85   $95.80  
  Purchase #3 $175.83   8.439%   $190.6683   $190.67   $190.65   $190.70  
  Purchase #4 $87.82   6.825%   $93.8137   $93.81   $93.80   $93.80  
  Purchase #5 $166.41   8.494%   $180.5449   $180.54   $180.55   $180.50  
  Purchase #6 $68.96   10.254%   $76.0312   $76.03   $76.05   $76.00  
  Purchase #7 $82.77   3.468%   $85.6405   $85.64   $85.65   $85.60  
  7 purchase totals = $775.00       $842.2878   $842.28   $842.30   $842.10