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 $102.77   11.685%   $114.7787   $114.78   $114.80   $114.80  
  Purchase #2 $205.41   12.471%   $231.0267   $231.03   $231.05   $231.00  
  Purchase #3 $158.64   12.441%   $178.3764   $178.38   $178.40   $178.40  
  Purchase #4 $228.59   12.848%   $257.9592   $257.96   $257.95   $258.00  
  Purchase #5 $115.32   8.552%   $125.1822   $125.18   $125.20   $125.20  
  Purchase #6 $78.71   11.233%   $87.5515   $87.55   $87.55   $87.60  
  Purchase #7 $166.96   8.614%   $181.3419   $181.34   $181.35   $181.30  
  7 purchase totals = $1,056.40       $1,176.2166   $1,176.22   $1,176.30   $1,176.30