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 $72.83   5.278%   $76.674   $76.67   $76.65   $76.70  
  Purchase #2 $8.70   11.757%   $9.7229   $9.72   $9.70   $9.70  
  Purchase #3 $222.35   8.662%   $241.61   $241.61   $241.60   $241.60  
  Purchase #4 $61.58   13.350%   $69.8009   $69.80   $69.80   $69.80  
  Purchase #5 $104.86   12.858%   $118.3429   $118.34   $118.35   $118.30  
  Purchase #6 $127.64   12.317%   $143.3614   $143.36   $143.35   $143.40  
  Purchase #7 $226.25   4.564%   $236.5761   $236.58   $236.60   $236.60  
  7 purchase totals = $824.21       $896.0882   $896.08   $896.05   $896.10