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 $34.76   9.283%   $37.9868   $37.99   $38.00   $38.00  
  Purchase #2 $218.31   13.522%   $247.8299   $247.83   $247.85   $247.80  
  Purchase #3 $164.78   6.627%   $175.7   $175.70   $175.70   $175.70  
  Purchase #4 $214.92   4.206%   $223.9595   $223.96   $223.95   $224.00  
  Purchase #5 $159.81   4.411%   $166.8592   $166.86   $166.85   $166.90  
  Purchase #6 $227.33   4.817%   $238.2805   $238.28   $238.30   $238.30  
  Purchase #7 $111.41   3.673%   $115.5021   $115.50   $115.50   $115.50  
  7 purchase totals = $1,131.32       $1,206.1180   $1,206.12   $1,206.15   $1,206.20