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 $24.92   4.362%   $26.007   $26.01   $26.00   $26.00  
  Purchase #2 $27.94   12.160%   $31.3375   $31.34   $31.35   $31.30  
  Purchase #3 $122.91   3.531%   $127.25   $127.25   $127.25   $127.30  
  Purchase #4 $169.64   9.854%   $186.3563   $186.36   $186.35   $186.40  
  Purchase #5 $217.45   4.280%   $226.7569   $226.76   $226.75   $226.80  
  Purchase #6 $39.93   8.451%   $43.3045   $43.30   $43.30   $43.30  
  Purchase #7 $177.63   3.249%   $183.4012   $183.40   $183.40   $183.40  
  7 purchase totals = $780.42       $824.4134   $824.42   $824.40   $824.50