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 $138.39   5.366%   $145.816   $145.82   $145.80   $145.80  
  Purchase #2 $205.71   12.522%   $231.469   $231.47   $231.45   $231.50  
  Purchase #3 $96.99   13.763%   $110.3387   $110.34   $110.35   $110.30  
  Purchase #4 $241.60   8.758%   $262.7593   $262.76   $262.75   $262.80  
  Purchase #5 $46.67   3.721%   $48.4066   $48.41   $48.40   $48.40  
  Purchase #6 $56.35   12.123%   $63.1813   $63.18   $63.20   $63.20  
  Purchase #7 $150.68   13.655%   $171.2554   $171.26   $171.25   $171.30  
  7 purchase totals = $936.39       $1,033.2263   $1,033.24   $1,033.20   $1,033.30