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 $234.76   7.569%   $252.529   $252.53   $252.55   $252.50  
  Purchase #2 $230.99   3.795%   $239.7561   $239.76   $239.75   $239.80  
  Purchase #3 $73.54   7.198%   $78.8334   $78.83   $78.85   $78.80  
  Purchase #4 $52.34   6.181%   $55.5751   $55.58   $55.60   $55.60  
  Purchase #5 $32.62   7.528%   $35.0756   $35.08   $35.10   $35.10  
  Purchase #6 $119.43   11.851%   $133.5836   $133.58   $133.60   $133.60  
  Purchase #7 $192.37   6.812%   $205.4742   $205.47   $205.45   $205.50  
  7 purchase totals = $936.05       $1,000.8270   $1,000.83   $1,000.90   $1,000.90