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 $239.49   11.355%   $266.6841   $266.68   $266.70   $266.70  
  Purchase #2 $171.95   3.317%   $177.6536   $177.65   $177.65   $177.70  
  Purchase #3 $10.82   10.328%   $11.9375   $11.94   $11.95   $11.90  
  Purchase #4 $199.57   10.461%   $220.447   $220.45   $220.45   $220.40  
  Purchase #5 $174.88   6.142%   $185.6211   $185.62   $185.60   $185.60  
  Purchase #6 $160.73   5.291%   $169.2342   $169.23   $169.25   $169.20  
  Purchase #7 $60.35   8.629%   $65.5576   $65.56   $65.55   $65.60  
  7 purchase totals = $1,017.79       $1,097.1351   $1,097.13   $1,097.15   $1,097.10