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 $238.49   11.119%   $265.0077   $265.01   $265.00   $265.00  
  Purchase #2 $32.70   7.718%   $35.2238   $35.22   $35.20   $35.20  
  Purchase #3 $70.92   13.451%   $80.4594   $80.46   $80.45   $80.50  
  Purchase #4 $35.93   10.238%   $39.6085   $39.61   $39.60   $39.60  
  Purchase #5 $229.85   6.464%   $244.7075   $244.71   $244.70   $244.70  
  Purchase #6 $201.40   4.320%   $210.1005   $210.10   $210.10   $210.10  
  Purchase #7 $155.99   6.477%   $166.0935   $166.09   $166.10   $166.10  
  7 purchase totals = $965.28       $1,041.2009   $1,041.20   $1,041.15   $1,041.20