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 $179.70   10.643%   $198.8255   $198.83   $198.85   $198.80  
  Purchase #2 $206.49   8.833%   $224.7293   $224.73   $224.75   $224.70  
  Purchase #3 $218.97   13.656%   $248.8725   $248.87   $248.85   $248.90  
  Purchase #4 $82.82   3.741%   $85.9183   $85.92   $85.90   $85.90  
  Purchase #5 $150.87   13.336%   $170.99   $170.99   $171.00   $171.00  
  Purchase #6 $227.81   13.585%   $258.758   $258.76   $258.75   $258.80  
  Purchase #7 $155.82   5.568%   $164.4961   $164.50   $164.50   $164.50  
  7 purchase totals = $1,222.48       $1,352.5897   $1,352.60   $1,352.60   $1,352.60