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 $64.99   10.262%   $71.6593   $71.66   $71.65   $71.70  
  Purchase #2 $163.69   9.475%   $179.1996   $179.20   $179.20   $179.20  
  Purchase #3 $109.56   7.361%   $117.6247   $117.62   $117.60   $117.60  
  Purchase #4 $31.34   7.690%   $33.75   $33.75   $33.75   $33.80  
  Purchase #5 $151.58   13.772%   $172.4556   $172.46   $172.45   $172.50  
  Purchase #6 $5.46   11.524%   $6.0892   $6.09   $6.10   $6.10  
  Purchase #7 $25.28   4.606%   $26.4444   $26.44   $26.45   $26.40  
  7 purchase totals = $551.90       $607.2228   $607.22   $607.20   $607.30