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 $241.77   8.149%   $261.4718   $261.47   $261.45   $261.50  
  Purchase #2 $165.62   7.648%   $178.2866   $178.29   $178.30   $178.30  
  Purchase #3 $153.43   4.343%   $160.0935   $160.09   $160.10   $160.10  
  Purchase #4 $58.33   12.623%   $65.693   $65.69   $65.70   $65.70  
  Purchase #5 $190.32   9.293%   $208.0064   $208.01   $208.00   $208.00  
  Purchase #6 $173.76   7.860%   $187.4175   $187.42   $187.40   $187.40  
  Purchase #7 $144.55   9.843%   $158.7781   $158.78   $158.80   $158.80  
  7 purchase totals = $1,127.78       $1,219.7469   $1,219.75   $1,219.75   $1,219.80