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 $64.34   8.729%   $69.9562   $69.96   $69.95   $70.00  
  Purchase #2 $50.63   12.264%   $56.8393   $56.84   $56.85   $56.80  
  Purchase #3 $238.82   6.277%   $253.8107   $253.81   $253.80   $253.80  
  Purchase #4 $213.82   9.425%   $233.9725   $233.97   $233.95   $234.00  
  Purchase #5 $124.75   12.171%   $139.9333   $139.93   $139.95   $139.90  
  Purchase #6 $32.79   6.329%   $34.8653   $34.87   $34.85   $34.90  
  Purchase #7 $137.99   5.745%   $145.9175   $145.92   $145.90   $145.90  
  7 purchase totals = $863.14       $935.2948   $935.30   $935.25   $935.30