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 $218.86   8.239%   $236.8919   $236.89   $236.90   $236.90  
  Purchase #2 $152.37   7.842%   $164.3189   $164.32   $164.30   $164.30  
  Purchase #3 $32.91   6.392%   $35.0136   $35.01   $35.00   $35.00  
  Purchase #4 $241.44   8.136%   $261.0836   $261.08   $261.10   $261.10  
  Purchase #5 $185.42   3.626%   $192.1433   $192.14   $192.15   $192.10  
  Purchase #6 $151.37   11.650%   $169.0046   $169.00   $169.00   $169.00  
  Purchase #7 $49.77   5.226%   $52.371   $52.37   $52.35   $52.40  
  7 purchase totals = $1,032.14       $1,110.8269   $1,110.81   $1,110.80   $1,110.80