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 $26.58   11.460%   $29.6261   $29.63   $29.65   $29.60  
  Purchase #2 $228.96   12.312%   $257.1496   $257.15   $257.15   $257.10  
  Purchase #3 $23.83   13.288%   $26.9965   $27.00   $27.00   $27.00  
  Purchase #4 $78.34   7.162%   $83.9507   $83.95   $83.95   $84.00  
  Purchase #5 $122.89   13.814%   $139.866   $139.87   $139.85   $139.90  
  Purchase #6 $220.51   10.788%   $244.2986   $244.30   $244.30   $244.30  
  Purchase #7 $141.72   4.831%   $148.5665   $148.57   $148.55   $148.60  
  7 purchase totals = $842.83       $930.4540   $930.47   $930.45   $930.50