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 $206.48   8.491%   $224.0122   $224.01   $224.00   $224.00  
  Purchase #2 $112.50   11.285%   $125.1956   $125.20   $125.20   $125.20  
  Purchase #3 $74.38   9.805%   $81.673   $81.67   $81.65   $81.70  
  Purchase #4 $229.65   8.178%   $248.4308   $248.43   $248.45   $248.40  
  Purchase #5 $45.55   3.534%   $47.1597   $47.16   $47.15   $47.20  
  Purchase #6 $245.70   4.448%   $256.6287   $256.63   $256.65   $256.60  
  Purchase #7 $50.69   8.534%   $55.0159   $55.02   $55.00   $55.00  
  7 purchase totals = $964.95       $1,038.1159   $1,038.12   $1,038.10   $1,038.10