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 $41.72   6.469%   $44.4189   $44.42   $44.40   $44.40  
  Purchase #2 $102.72   11.807%   $114.8482   $114.85   $114.85   $114.80  
  Purchase #3 $50.33   6.356%   $53.529   $53.53   $53.55   $53.50  
  Purchase #4 $179.99   3.180%   $185.7137   $185.71   $185.70   $185.70  
  Purchase #5 $150.35   11.589%   $167.7741   $167.77   $167.75   $167.80  
  Purchase #6 $110.25   10.526%   $121.8549   $121.85   $121.85   $121.90  
  Purchase #7 $64.64   7.393%   $69.4188   $69.42   $69.40   $69.40  
  7 purchase totals = $700.00       $757.5576   $757.55   $757.50   $757.50