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 $39.66   10.105%   $43.6676   $43.67   $43.65   $43.70  
  Purchase #2 $13.81   3.788%   $14.3331   $14.33   $14.35   $14.30  
  Purchase #3 $49.38   9.262%   $53.9536   $53.95   $53.95   $54.00  
  Purchase #4 $245.99   6.742%   $262.5746   $262.57   $262.55   $262.60  
  Purchase #5 $176.32   5.164%   $185.4252   $185.43   $185.45   $185.40  
  Purchase #6 $119.40   7.301%   $128.1174   $128.12   $128.10   $128.10  
  Purchase #7 $203.54   7.571%   $218.95   $218.95   $218.95   $219.00  
  7 purchase totals = $848.10       $907.0215   $907.02   $907.00   $907.10