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 $32.71   13.642%   $37.1723   $37.17   $37.15   $37.20  
  Purchase #2 $226.73   8.798%   $246.6777   $246.68   $246.70   $246.70  
  Purchase #3 $103.90   13.773%   $118.2101   $118.21   $118.20   $118.20  
  Purchase #4 $67.70   12.668%   $76.2762   $76.28   $76.30   $76.30  
  Purchase #5 $141.74   3.113%   $146.1524   $146.15   $146.15   $146.20  
  Purchase #6 $164.76   4.641%   $172.4065   $172.41   $172.40   $172.40  
  Purchase #7 $250.66   3.589%   $259.6562   $259.66   $259.65   $259.70  
  7 purchase totals = $988.20       $1,056.5514   $1,056.56   $1,056.55   $1,056.70