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 $176.82   13.440%   $200.5846   $200.58   $200.60   $200.60  
  Purchase #2 $24.47   6.394%   $26.0346   $26.03   $26.05   $26.00  
  Purchase #3 $90.32   5.287%   $95.0952   $95.10   $95.10   $95.10  
  Purchase #4 $230.46   11.672%   $257.3593   $257.36   $257.35   $257.40  
  Purchase #5 $103.69   12.312%   $116.4563   $116.46   $116.45   $116.50  
  Purchase #6 $9.59   9.639%   $10.5144   $10.51   $10.50   $10.50  
  Purchase #7 $127.68   12.231%   $143.2965   $143.30   $143.30   $143.30  
  7 purchase totals = $763.03       $849.3409   $849.34   $849.35   $849.40