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 $186.67   10.452%   $206.1807   $206.18   $206.20   $206.20  
  Purchase #2 $183.64   11.161%   $204.1361   $204.14   $204.15   $204.10  
  Purchase #3 $66.79   13.510%   $75.8133   $75.81   $75.80   $75.80  
  Purchase #4 $162.93   5.360%   $171.663   $171.66   $171.65   $171.70  
  Purchase #5 $250.45   8.594%   $271.9737   $271.97   $271.95   $272.00  
  Purchase #6 $162.96   12.845%   $183.8922   $183.89   $183.90   $183.90  
  Purchase #7 $144.35   7.106%   $154.6075   $154.61   $154.60   $154.60  
  7 purchase totals = $1,157.79       $1,268.2665   $1,268.26   $1,268.25   $1,268.30