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 $58.63   12.108%   $65.7289   $65.73   $65.75   $65.70  
  Purchase #2 $226.33   7.769%   $243.9136   $243.91   $243.90   $243.90  
  Purchase #3 $222.31   13.418%   $252.1396   $252.14   $252.15   $252.10  
  Purchase #4 $196.67   12.666%   $221.5802   $221.58   $221.60   $221.60  
  Purchase #5 $114.32   10.546%   $126.3762   $126.38   $126.40   $126.40  
  Purchase #6 $100.95   13.395%   $114.4723   $114.47   $114.45   $114.50  
  Purchase #7 $197.96   3.501%   $204.8906   $204.89   $204.90   $204.90  
  7 purchase totals = $1,117.17       $1,229.1014   $1,229.10   $1,229.15   $1,229.10