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 $140.25   10.245%   $154.6186   $154.62   $154.60   $154.60  
  Purchase #2 $215.61   11.716%   $240.8709   $240.87   $240.85   $240.90  
  Purchase #3 $149.64   11.742%   $167.2107   $167.21   $167.20   $167.20  
  Purchase #4 $202.66   11.541%   $226.049   $226.05   $226.05   $226.00  
  Purchase #5 $177.77   7.420%   $190.9605   $190.96   $190.95   $191.00  
  Purchase #6 $215.65   8.300%   $233.549   $233.55   $233.55   $233.50  
  Purchase #7 $65.74   10.186%   $72.4363   $72.44   $72.45   $72.40  
  7 purchase totals = $1,167.32       $1,285.6950   $1,285.70   $1,285.65   $1,285.60