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 $105.36   10.685%   $116.6177   $116.62   $116.60   $116.60  
  Purchase #2 $199.97   7.156%   $214.2799   $214.28   $214.30   $214.30  
  Purchase #3 $156.58   13.716%   $178.0565   $178.06   $178.05   $178.10  
  Purchase #4 $172.41   8.630%   $187.289   $187.29   $187.30   $187.30  
  Purchase #5 $106.55   12.657%   $120.036   $120.04   $120.05   $120.00  
  Purchase #6 $237.46   10.323%   $261.973   $261.97   $261.95   $262.00  
  Purchase #7 $155.65   11.768%   $173.9669   $173.97   $173.95   $174.00  
  7 purchase totals = $1,133.98       $1,252.2190   $1,252.23   $1,252.20   $1,252.30