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 $241.62   8.718%   $262.6844   $262.68   $262.70   $262.70  
  Purchase #2 $162.98   11.720%   $182.0813   $182.08   $182.10   $182.10  
  Purchase #3 $168.37   7.287%   $180.6391   $180.64   $180.65   $180.60  
  Purchase #4 $33.70   10.702%   $37.3066   $37.31   $37.30   $37.30  
  Purchase #5 $236.60   12.746%   $266.757   $266.76   $266.75   $266.80  
  Purchase #6 $170.91   3.535%   $176.9517   $176.95   $176.95   $177.00  
  Purchase #7 $162.88   11.829%   $182.1471   $182.15   $182.15   $182.10  
  7 purchase totals = $1,177.06       $1,288.5672   $1,288.57   $1,288.60   $1,288.60