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 $39.27   6.328%   $41.755   $41.76   $41.75   $41.80  
  Purchase #2 $195.75   9.656%   $214.6516   $214.65   $214.65   $214.70  
  Purchase #3 $60.51   3.475%   $62.6127   $62.61   $62.60   $62.60  
  Purchase #4 $247.75   10.542%   $273.8678   $273.87   $273.85   $273.90  
  Purchase #5 $85.48   10.310%   $94.293   $94.29   $94.30   $94.30  
  Purchase #6 $95.75   5.161%   $100.6917   $100.69   $100.70   $100.70  
  Purchase #7 $207.58   4.672%   $217.2781   $217.28   $217.30   $217.30  
  7 purchase totals = $932.09       $1,005.1499   $1,005.15   $1,005.15   $1,005.30