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 $61.55   3.763%   $63.8661   $63.87   $63.85   $63.90  
  Purchase #2 $73.87   13.354%   $83.7346   $83.73   $83.75   $83.70  
  Purchase #3 $239.79   9.180%   $261.8027   $261.80   $261.80   $261.80  
  Purchase #4 $212.87   10.684%   $235.613   $235.61   $235.60   $235.60  
  Purchase #5 $164.28   10.398%   $181.3618   $181.36   $181.35   $181.40  
  Purchase #6 $107.26   10.150%   $118.1469   $118.15   $118.15   $118.10  
  Purchase #7 $193.63   3.466%   $200.3412   $200.34   $200.35   $200.30  
  7 purchase totals = $1,053.25       $1,144.8663   $1,144.86   $1,144.85   $1,144.80