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 $157.86   6.592%   $168.2661   $168.27   $168.25   $168.30  
  Purchase #2 $50.93   10.334%   $56.1931   $56.19   $56.20   $56.20  
  Purchase #3 $19.72   11.570%   $22.0016   $22.00   $22.00   $22.00  
  Purchase #4 $250.64   6.161%   $266.0819   $266.08   $266.10   $266.10  
  Purchase #5 $109.73   4.122%   $114.2531   $114.25   $114.25   $114.30  
  Purchase #6 $212.99   6.288%   $226.3828   $226.38   $226.40   $226.40  
  Purchase #7 $178.27   13.335%   $202.0423   $202.04   $202.05   $202.00  
  7 purchase totals = $980.14       $1,055.2209   $1,055.21   $1,055.25   $1,055.30