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 $43.34   3.157%   $44.7082   $44.71   $44.70   $44.70  
  Purchase #2 $212.70   5.231%   $223.8263   $223.83   $223.85   $223.80  
  Purchase #3 $150.94   6.695%   $161.0454   $161.05   $161.05   $161.00  
  Purchase #4 $114.27   9.447%   $125.0651   $125.07   $125.05   $125.10  
  Purchase #5 $56.40   3.514%   $58.3819   $58.38   $58.40   $58.40  
  Purchase #6 $175.59   9.493%   $192.2588   $192.26   $192.25   $192.30  
  Purchase #7 $226.77   11.554%   $252.971   $252.97   $252.95   $253.00  
  7 purchase totals = $980.01       $1,058.2567   $1,058.27   $1,058.25   $1,058.30