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 $195.26   12.276%   $219.2301   $219.23   $219.25   $219.20  
  Purchase #2 $102.83   10.671%   $113.803   $113.80   $113.80   $113.80  
  Purchase #3 $77.63   5.438%   $81.8515   $81.85   $81.85   $81.90  
  Purchase #4 $220.31   6.457%   $234.5354   $234.54   $234.55   $234.50  
  Purchase #5 $250.46   13.734%   $284.8582   $284.86   $284.85   $284.90  
  Purchase #6 $115.63   11.691%   $129.1483   $129.15   $129.15   $129.10  
  Purchase #7 $151.79   11.434%   $169.1457   $169.15   $169.15   $169.10  
  7 purchase totals = $1,113.91       $1,232.5722   $1,232.58   $1,232.60   $1,232.50