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 $177.45   11.361%   $197.6101   $197.61   $197.60   $197.60  
  Purchase #2 $59.81   10.106%   $65.8544   $65.85   $65.85   $65.90  
  Purchase #3 $118.69   5.214%   $124.8785   $124.88   $124.90   $124.90  
  Purchase #4 $115.26   9.347%   $126.0334   $126.03   $126.05   $126.00  
  Purchase #5 $231.77   9.640%   $254.1126   $254.11   $254.10   $254.10  
  Purchase #6 $86.79   12.214%   $97.3905   $97.39   $97.40   $97.40  
  Purchase #7 $124.54   10.277%   $137.339   $137.34   $137.35   $137.30  
  7 purchase totals = $914.31       $1,003.2185   $1,003.21   $1,003.25   $1,003.20