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 $148.32   10.239%   $163.5065   $163.51   $163.50   $163.50  
  Purchase #2 $155.98   11.678%   $174.1953   $174.20   $174.20   $174.20  
  Purchase #3 $65.31   3.710%   $67.733   $67.73   $67.75   $67.70  
  Purchase #4 $35.43   10.729%   $39.2313   $39.23   $39.25   $39.20  
  Purchase #5 $82.48   3.725%   $85.5524   $85.55   $85.55   $85.60  
  Purchase #6 $91.53   6.244%   $97.2451   $97.25   $97.25   $97.20  
  Purchase #7 $130.78   10.292%   $144.2399   $144.24   $144.25   $144.20  
  7 purchase totals = $709.83       $771.7035   $771.71   $771.75   $771.60