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 $246.58   9.471%   $269.9336   $269.93   $269.95   $269.90  
  Purchase #2 $223.99   9.672%   $245.6543   $245.65   $245.65   $245.70  
  Purchase #3 $44.91   8.825%   $48.8733   $48.87   $48.85   $48.90  
  Purchase #4 $184.42   7.439%   $198.139   $198.14   $198.15   $198.10  
  Purchase #5 $129.83   3.363%   $134.1962   $134.20   $134.20   $134.20  
  Purchase #6 $27.99   6.806%   $29.895   $29.90   $29.90   $29.90  
  Purchase #7 $32.76   4.535%   $34.2457   $34.25   $34.25   $34.20  
  7 purchase totals = $890.48       $960.9371   $960.94   $960.95   $960.90