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 $175.91   4.855%   $184.4504   $184.45   $184.45   $184.50  
  Purchase #2 $126.72   8.633%   $137.6597   $137.66   $137.65   $137.70  
  Purchase #3 $39.45   10.327%   $43.524   $43.52   $43.50   $43.50  
  Purchase #4 $246.50   7.631%   $265.3104   $265.31   $265.30   $265.30  
  Purchase #5 $214.95   6.298%   $228.4876   $228.49   $228.50   $228.50  
  Purchase #6 $179.26   10.861%   $198.7294   $198.73   $198.75   $198.70  
  Purchase #7 $152.62   10.423%   $168.5276   $168.53   $168.55   $168.50  
  7 purchase totals = $1,135.41       $1,226.6891   $1,226.69   $1,226.70   $1,226.70