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 $201.58   12.426%   $226.6283   $226.63   $226.65   $226.60  
  Purchase #2 $179.85   3.200%   $185.6052   $185.61   $185.60   $185.60  
  Purchase #3 $18.71   9.217%   $20.4345   $20.43   $20.45   $20.40  
  Purchase #4 $56.85   6.429%   $60.5049   $60.50   $60.50   $60.50  
  Purchase #5 $250.69   3.318%   $259.0079   $259.01   $259.00   $259.00  
  Purchase #6 $23.46   8.556%   $25.4672   $25.47   $25.45   $25.50  
  Purchase #7 $166.46   9.746%   $182.6832   $182.68   $182.70   $182.70  
  7 purchase totals = $897.60       $960.3312   $960.33   $960.35   $960.30