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 $219.96   8.770%   $239.2505   $239.25   $239.25   $239.30  
  Purchase #2 $76.26   13.466%   $86.5292   $86.53   $86.55   $86.50  
  Purchase #3 $120.62   8.292%   $130.6218   $130.62   $130.60   $130.60  
  Purchase #4 $71.33   7.656%   $76.791   $76.79   $76.80   $76.80  
  Purchase #5 $136.56   7.425%   $146.6996   $146.70   $146.70   $146.70  
  Purchase #6 $232.90   7.519%   $250.4118   $250.41   $250.40   $250.40  
  Purchase #7 $74.91   8.237%   $81.0803   $81.08   $81.10   $81.10  
  7 purchase totals = $932.54       $1,011.3842   $1,011.38   $1,011.40   $1,011.40