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 $60.25   12.272%   $67.6439   $67.64   $67.65   $67.60  
  Purchase #2 $25.30   3.598%   $26.2103   $26.21   $26.20   $26.20  
  Purchase #3 $192.33   5.522%   $202.9505   $202.95   $202.95   $203.00  
  Purchase #4 $226.69   9.265%   $247.6928   $247.69   $247.70   $247.70  
  Purchase #5 $86.41   5.535%   $91.1928   $91.19   $91.20   $91.20  
  Purchase #6 $139.60   12.318%   $156.7959   $156.80   $156.80   $156.80  
  Purchase #7 $81.99   5.173%   $86.2313   $86.23   $86.25   $86.20  
  7 purchase totals = $812.57       $878.7175   $878.71   $878.75   $878.70