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 $239.30   11.240%   $266.1973   $266.20   $266.20   $266.20  
  Purchase #2 $180.47   12.458%   $202.953   $202.95   $202.95   $203.00  
  Purchase #3 $32.67   7.553%   $35.1376   $35.14   $35.15   $35.10  
  Purchase #4 $135.77   8.461%   $147.2575   $147.26   $147.25   $147.30  
  Purchase #5 $150.61   8.864%   $163.9601   $163.96   $163.95   $164.00  
  Purchase #6 $176.50   3.574%   $182.8081   $182.81   $182.80   $182.80  
  Purchase #7 $155.53   12.338%   $174.7193   $174.72   $174.70   $174.70  
  7 purchase totals = $1,070.85       $1,173.0329   $1,173.04   $1,173.00   $1,173.10