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 $189.29   12.656%   $213.2465   $213.25   $213.25   $213.20  
  Purchase #2 $205.41   9.514%   $224.9527   $224.95   $224.95   $225.00  
  Purchase #3 $141.42   3.673%   $146.6144   $146.61   $146.60   $146.60  
  Purchase #4 $163.49   8.642%   $177.6188   $177.62   $177.60   $177.60  
  Purchase #5 $208.66   12.139%   $233.9892   $233.99   $234.00   $234.00  
  Purchase #6 $188.45   3.119%   $194.3278   $194.33   $194.35   $194.30  
  Purchase #7 $173.64   10.839%   $192.4608   $192.46   $192.45   $192.50  
  7 purchase totals = $1,270.36       $1,383.2102   $1,383.21   $1,383.20   $1,383.20