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 $244.39   9.842%   $268.4429   $268.44   $268.45   $268.40  
  Purchase #2 $232.68   8.688%   $252.8952   $252.90   $252.90   $252.90  
  Purchase #3 $87.56   5.376%   $92.2672   $92.27   $92.25   $92.30  
  Purchase #4 $72.48   5.771%   $76.6628   $76.66   $76.65   $76.70  
  Purchase #5 $191.85   10.786%   $212.5429   $212.54   $212.55   $212.50  
  Purchase #6 $72.32   5.849%   $76.55   $76.55   $76.55   $76.60  
  Purchase #7 $141.96   11.499%   $158.284   $158.28   $158.30   $158.30  
  7 purchase totals = $1,043.24       $1,137.6450   $1,137.64   $1,137.65   $1,137.70