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 $237.69   10.196%   $261.9249   $261.92   $261.90   $261.90  
  Purchase #2 $90.93   3.780%   $94.3672   $94.37   $94.35   $94.40  
  Purchase #3 $167.70   5.442%   $176.8262   $176.83   $176.85   $176.80  
  Purchase #4 $34.29   12.657%   $38.6301   $38.63   $38.65   $38.60  
  Purchase #5 $160.96   10.595%   $178.0137   $178.01   $178.00   $178.00  
  Purchase #6 $146.55   9.839%   $160.9691   $160.97   $160.95   $161.00  
  Purchase #7 $143.58   10.424%   $158.5468   $158.55   $158.55   $158.50  
  7 purchase totals = $981.70       $1,069.2780   $1,069.28   $1,069.25   $1,069.20