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 $74.56   10.762%   $82.5841   $82.58   $82.60   $82.60  
  Purchase #2 $180.33   3.357%   $186.3837   $186.38   $186.40   $186.40  
  Purchase #3 $129.88   4.337%   $135.5129   $135.51   $135.50   $135.50  
  Purchase #4 $204.90   11.623%   $228.7155   $228.72   $228.70   $228.70  
  Purchase #5 $11.57   6.531%   $12.3256   $12.33   $12.35   $12.30  
  Purchase #6 $151.74   6.159%   $161.0857   $161.09   $161.10   $161.10  
  Purchase #7 $224.71   12.271%   $252.2842   $252.28   $252.30   $252.30  
  7 purchase totals = $977.69       $1,058.8917   $1,058.89   $1,058.95   $1,058.90