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 $24.81   3.597%   $25.7024   $25.70   $25.70   $25.70  
  Purchase #2 $94.51   9.519%   $103.5064   $103.51   $103.50   $103.50  
  Purchase #3 $81.38   6.524%   $86.6892   $86.69   $86.70   $86.70  
  Purchase #4 $7.72   3.309%   $7.9755   $7.98   $8.00   $8.00  
  Purchase #5 $87.94   8.412%   $95.3375   $95.34   $95.35   $95.30  
  Purchase #6 $87.75   3.192%   $90.551   $90.55   $90.55   $90.60  
  Purchase #7 $95.97   10.690%   $106.2292   $106.23   $106.25   $106.20  
  7 purchase totals = $480.08       $515.9912   $516.00   $516.05   $516.00