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 $183.63   13.266%   $207.9904   $207.99   $208.00   $208.00  
  Purchase #2 $73.61   4.648%   $77.0314   $77.03   $77.05   $77.00  
  Purchase #3 $221.69   5.810%   $234.5702   $234.57   $234.55   $234.60  
  Purchase #4 $101.99   4.748%   $106.8325   $106.83   $106.85   $106.80  
  Purchase #5 $172.42   3.863%   $179.0806   $179.08   $179.10   $179.10  
  Purchase #6 $138.55   12.461%   $155.8147   $155.81   $155.80   $155.80  
  Purchase #7 $203.82   3.306%   $210.5583   $210.56   $210.55   $210.60  
  7 purchase totals = $1,095.71       $1,171.8781   $1,171.87   $1,171.90   $1,171.90