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 $78.65   9.691%   $86.272   $86.27   $86.25   $86.30  
  Purchase #2 $107.87   10.442%   $119.1338   $119.13   $119.15   $119.10  
  Purchase #3 $70.40   12.616%   $79.2817   $79.28   $79.30   $79.30  
  Purchase #4 $183.97   12.301%   $206.6001   $206.60   $206.60   $206.60  
  Purchase #5 $241.51   4.409%   $252.1582   $252.16   $252.15   $252.20  
  Purchase #6 $60.54   11.246%   $67.3483   $67.35   $67.35   $67.30  
  Purchase #7 $250.39   7.387%   $268.8863   $268.89   $268.90   $268.90  
  7 purchase totals = $993.33       $1,079.6804   $1,079.68   $1,079.70   $1,079.70