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 $114.69   5.312%   $120.7823   $120.78   $120.80   $120.80  
  Purchase #2 $101.92   10.748%   $112.8744   $112.87   $112.85   $112.90  
  Purchase #3 $230.79   7.483%   $248.06   $248.06   $248.05   $248.10  
  Purchase #4 $95.81   9.274%   $104.6954   $104.70   $104.70   $104.70  
  Purchase #5 $168.51   5.724%   $178.1555   $178.16   $178.15   $178.20  
  Purchase #6 $241.25   5.256%   $253.9301   $253.93   $253.95   $253.90  
  Purchase #7 $202.29   5.154%   $212.716   $212.72   $212.70   $212.70  
  7 purchase totals = $1,155.26       $1,231.2137   $1,231.22   $1,231.20   $1,231.30