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 $240.98   13.711%   $274.0208   $274.02   $274.00   $274.00  
  Purchase #2 $170.99   12.867%   $192.9913   $192.99   $193.00   $193.00  
  Purchase #3 $230.81   3.650%   $239.2346   $239.23   $239.25   $239.20  
  Purchase #4 $166.72   4.395%   $174.0473   $174.05   $174.05   $174.00  
  Purchase #5 $143.81   7.388%   $154.4347   $154.43   $154.45   $154.40  
  Purchase #6 $198.81   13.758%   $226.1623   $226.16   $226.15   $226.20  
  Purchase #7 $31.74   6.750%   $33.8825   $33.88   $33.90   $33.90  
  7 purchase totals = $1,183.86       $1,294.7735   $1,294.76   $1,294.80   $1,294.70