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 $242.32   10.523%   $267.8193   $267.82   $267.80   $267.80  
  Purchase #2 $55.67   4.691%   $58.2815   $58.28   $58.30   $58.30  
  Purchase #3 $114.91   5.426%   $121.145   $121.15   $121.15   $121.10  
  Purchase #4 $170.63   7.815%   $183.9647   $183.96   $183.95   $184.00  
  Purchase #5 $100.68   8.182%   $108.9176   $108.92   $108.90   $108.90  
  Purchase #6 $172.89   10.807%   $191.5742   $191.57   $191.55   $191.60  
  Purchase #7 $102.49   10.641%   $113.396   $113.40   $113.40   $113.40  
  7 purchase totals = $959.59       $1,045.0983   $1,045.10   $1,045.05   $1,045.10