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 $212.36   13.396%   $240.8077   $240.81   $240.80   $240.80  
  Purchase #2 $59.80   4.714%   $62.619   $62.62   $62.60   $62.60  
  Purchase #3 $63.57   7.243%   $68.1744   $68.17   $68.15   $68.20  
  Purchase #4 $212.30   11.743%   $237.2304   $237.23   $237.25   $237.20  
  Purchase #5 $11.66   9.457%   $12.7627   $12.76   $12.75   $12.80  
  Purchase #6 $8.47   4.395%   $8.8423   $8.84   $8.85   $8.80  
  Purchase #7 $205.75   12.836%   $232.1601   $232.16   $232.15   $232.20  
  7 purchase totals = $773.91       $862.5966   $862.59   $862.55   $862.60