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 $93.79   10.371%   $103.517   $103.52   $103.50   $103.50  
  Purchase #2 $249.78   4.743%   $261.6271   $261.63   $261.65   $261.60  
  Purchase #3 $227.94   5.560%   $240.6135   $240.61   $240.60   $240.60  
  Purchase #4 $140.41   13.711%   $159.6616   $159.66   $159.65   $159.70  
  Purchase #5 $71.68   3.509%   $74.1953   $74.20   $74.20   $74.20  
  Purchase #6 $32.61   7.525%   $35.0639   $35.06   $35.05   $35.10  
  Purchase #7 $171.43   5.739%   $181.2684   $181.27   $181.25   $181.30  
  7 purchase totals = $987.64       $1,055.9468   $1,055.95   $1,055.90   $1,056.00