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 $56.61   4.734%   $59.2899   $59.29   $59.30   $59.30  
  Purchase #2 $180.97   6.409%   $192.5684   $192.57   $192.55   $192.60  
  Purchase #3 $8.65   8.566%   $9.391   $9.39   $9.40   $9.40  
  Purchase #4 $122.97   9.180%   $134.2586   $134.26   $134.25   $134.30  
  Purchase #5 $207.64   12.301%   $233.1818   $233.18   $233.20   $233.20  
  Purchase #6 $157.29   13.759%   $178.9315   $178.93   $178.95   $178.90  
  Purchase #7 $239.52   9.164%   $261.4696   $261.47   $261.45   $261.50  
  7 purchase totals = $973.65       $1,069.0908   $1,069.09   $1,069.10   $1,069.20