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 $230.86   6.413%   $245.6651   $245.67   $245.65   $245.70  
  Purchase #2 $61.63   4.587%   $64.457   $64.46   $64.45   $64.50  
  Purchase #3 $58.69   4.363%   $61.2506   $61.25   $61.25   $61.30  
  Purchase #4 $156.47   3.632%   $162.153   $162.15   $162.15   $162.20  
  Purchase #5 $118.78   6.420%   $126.4057   $126.41   $126.40   $126.40  
  Purchase #6 $66.58   8.138%   $71.9983   $72.00   $72.00   $72.00  
  Purchase #7 $234.64   11.724%   $262.1492   $262.15   $262.15   $262.10  
  7 purchase totals = $927.65       $994.0789   $994.09   $994.05   $994.20