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 $29.41   11.385%   $32.7583   $32.76   $32.75   $32.80  
  Purchase #2 $60.68   5.143%   $63.8008   $63.80   $63.80   $63.80  
  Purchase #3 $139.93   6.598%   $149.1626   $149.16   $149.15   $149.20  
  Purchase #4 $170.40   12.833%   $192.2674   $192.27   $192.25   $192.30  
  Purchase #5 $151.33   9.301%   $165.4052   $165.41   $165.40   $165.40  
  Purchase #6 $81.26   6.706%   $86.7093   $86.71   $86.70   $86.70  
  Purchase #7 $62.99   7.748%   $67.8705   $67.87   $67.85   $67.90  
  7 purchase totals = $696.00       $757.9741   $757.98   $757.90   $758.10