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 $23.52   3.150%   $24.2609   $24.26   $24.25   $24.30  
  Purchase #2 $201.86   12.784%   $227.6658   $227.67   $227.65   $227.70  
  Purchase #3 $123.78   8.587%   $134.409   $134.41   $134.40   $134.40  
  Purchase #4 $223.98   10.201%   $246.8282   $246.83   $246.85   $246.80  
  Purchase #5 $16.63   3.772%   $17.2573   $17.26   $17.25   $17.30  
  Purchase #6 $190.69   7.580%   $205.1443   $205.14   $205.15   $205.10  
  Purchase #7 $84.76   12.622%   $95.4584   $95.46   $95.45   $95.50  
  7 purchase totals = $865.22       $951.0239   $951.03   $951.00   $951.10