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 $105.65   13.104%   $119.4944   $119.49   $119.50   $119.50  
  Purchase #2 $207.89   7.177%   $222.8103   $222.81   $222.80   $222.80  
  Purchase #3 $42.93   11.820%   $48.0043   $48.00   $48.00   $48.00  
  Purchase #4 $215.61   7.557%   $231.9036   $231.90   $231.90   $231.90  
  Purchase #5 $225.42   11.279%   $250.8451   $250.85   $250.85   $250.80  
  Purchase #6 $248.27   9.571%   $272.0319   $272.03   $272.05   $272.00  
  Purchase #7 $195.62   8.447%   $212.144   $212.14   $212.15   $212.10  
  7 purchase totals = $1,241.39       $1,357.2336   $1,357.22   $1,357.25   $1,357.10