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 $152.69   9.546%   $167.2658   $167.27   $167.25   $167.30  
  Purchase #2 $228.51   8.367%   $247.6294   $247.63   $247.65   $247.60  
  Purchase #3 $159.83   3.594%   $165.5743   $165.57   $165.55   $165.60  
  Purchase #4 $26.80   11.244%   $29.8134   $29.81   $29.80   $29.80  
  Purchase #5 $219.25   12.724%   $247.1474   $247.15   $247.15   $247.10  
  Purchase #6 $212.76   8.704%   $231.2786   $231.28   $231.30   $231.30  
  Purchase #7 $86.44   5.771%   $91.4285   $91.43   $91.45   $91.40  
  7 purchase totals = $1,086.28       $1,180.1374   $1,180.14   $1,180.15   $1,180.10