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 $5.80   3.533%   $6.0049   $6.00   $6.00   $6.00  
  Purchase #2 $169.82   12.501%   $191.0492   $191.05   $191.05   $191.00  
  Purchase #3 $109.86   6.604%   $117.1152   $117.12   $117.10   $117.10  
  Purchase #4 $226.40   10.788%   $250.824   $250.82   $250.80   $250.80  
  Purchase #5 $198.83   3.488%   $205.7652   $205.77   $205.75   $205.80  
  Purchase #6 $114.87   9.820%   $126.1502   $126.15   $126.15   $126.20  
  Purchase #7 $247.49   6.194%   $262.8195   $262.82   $262.80   $262.80  
  7 purchase totals = $1,073.07       $1,159.7282   $1,159.73   $1,159.65   $1,159.70