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 $226.86   11.154%   $252.164   $252.16   $252.15   $252.20  
  Purchase #2 $117.41   8.194%   $127.0306   $127.03   $127.05   $127.00  
  Purchase #3 $236.70   4.852%   $248.1847   $248.18   $248.20   $248.20  
  Purchase #4 $29.78   4.342%   $31.073   $31.07   $31.05   $31.10  
  Purchase #5 $94.63   5.816%   $100.1337   $100.13   $100.15   $100.10  
  Purchase #6 $98.91   9.729%   $108.533   $108.53   $108.55   $108.50  
  Purchase #7 $163.34   13.177%   $184.8633   $184.86   $184.85   $184.90  
  7 purchase totals = $967.63       $1,051.9823   $1,051.96   $1,052.00   $1,052.00